Perissodactyla

“ There is conceivable relationship between the rodents and Plesiadapsis-like primates.
The dominant Tiffanian herbivorous mammals were members of the Order Condylarthra. These primitive ungulates were diverse in both size and appearance. It is probable that later modern ungulates (Artiodactyla, Perissodactyla) evolved from the Condylarthra; however, there are no surviving members of this group. The Paleocene condylarths were mostly small animals and include such forms as Haplaletes, Litomylus, and Gidleyina. ”

“ Though, as has been pointed out, it is a fact that the hind-feet are often on a different plane of evolution from the fore-feet, it seems that this amount of difference does not characterise any Ungulate, not excepting the genus now under consideration.
The toes are very spreading. The pelvic girdle is of great strength and broadness. The femur, as in the Perissodactyles, has a well-developed third trochanter; but whereas in this particular the hind-limb is Perissodactyle, it is Artiodactyle in the fact that the tibia and the fibula articulate with the astragalus and calcaneum. ”

“ The artiodactyls are and for a very long time have been a very much larger and more variegated group than the perissodactyls, and the Old World has been and still is their headquarters and area of special development, where they are represented in far greater number and variety than in the New; the perissodactyls, on the other hand, flourished especially in North America, as was shown in the preceding chapter. ”

“ In the first place, the tracing of the pedigrees of many groups of mammals has met with very considerable success; and it is clear that as we pass from the living Horse and Rhinoceros, with their complicated molars, to their forerunners, we find that both can be referred to a primitive Ungulate molar with but six cusps. Going still further back to the lowest Eocene and ancestral type as it appears, Euprotogonia, we still find in the molar tooth the sextubercular plan of structure. We can hardly get further back in the evolution of the Perissodactyles with any probability of security. ”

“ The main internal features of structure which divide this genus of Perissodactyles from the Rhinoceros or the Tapir, or from both, are: the existence of strong incisors, three on each side of each jaw; there are canines, but these are small and do not always persist in the full-grown mare. They are popularly known as "tusks" or "tushes." The first of the four premolars (the "wolf tooth") is small and quite rudimentary; it is often absent. As there are three molars, the present genus has the "typical" number of the Eutherian dentition, i.e. ”

“ A study of the skeleton, however, reveals the community of structure which obtains between the three families, a community which removes them widely from all other hoofed mammals. In all existing perissodactyls, though not in most of the Eocene genera, all the premolars, except the first, have the size and pattern of the molars. The foramina of the skull, or perforations by which blood-vessels and nerves enter and leave the cranium, are arranged in a way characteristic of the order and different from that seen in other hoofed mammals. The femur always has the third trochanter. ”

“ The anterior and posterior extremities are equally rounded. The peristome begins as a small depression, but becomes larger until it takes in nearly all of the ventral surface. The depression becomes much deeper at about the center of the body, and is especially marked on the left side of the peristome. In this deeper portion is the mouth, with an almost imperceptible œsophagus. Upon the left edge of the peristome is a high, undulating membrane, sail-like in appearance when extended. ”

“ It is therefore of particularly great importance that Dr Cognetti de Martiis should have met with the South American genus Periscolex which, undoubtedly a member of a totally distinct family, the Geoscolecidae, yet shows the same complete circle of setae. The reason for dwelling upon this particular anatomical character in the present connection is because it would seem to be a character specially suited to an underground life where there is an equal pressure all round the body and where progression would seem therefore to be best attained by a continual leverage round the circular body. ”

“ Sabelliformia.—The prostomium is entirely hidden by the forward extension of the peristomium; the tentacles are very small, being frequently represented merely by small knobs of sense-cells; the palps, on the other hand, are greatly developed, branched, and contain blood-vessels, acting as respiratory as well as sensory organs. The peristomium never carries cirri or chaetae, and it is usually raised up into a projecting collar, used in fashioning the lip of the animal's tube. The parapodia are but feebly developed ”

“ Abstract AbstractA new high altitude montane species of Trichostetha Burmeister, 1842 is described from the Elandsberg range of the Western Cape interior. This represents the 14th species of the genus and the first to be reported with a description of its larva. It is a significant addition to the growing number of species that exhibit no adult feeding behaviour and a short period of activity restricted to the onset of summer. Larvae dwell in rock crevices, feeding on decomposing plant matter. ”

“ In all Perichaetidae that are known the sperm-ducts open in common with the ducts of the spermiducal glands; they generally open into them at some distance from the common external pore. In Megascolex, Perichaeta, and Pleionogaster the nephridia are of the diffuse type so widely spread among these worms, and the spermiducal glands are lobate. Megascolex differs from the others in the fact that in addition to the small scattered nephridia there are a pair of large nephridia in each segment, and the chaetae do not form absolutely continuous circles, but are interrupted above and below. ”

“ Apart from the chaetae, there is no peculiarity in the organisation of the family Perichaetidae that is not also met with in the Cryptodrilidae. Even the highly characteristic intestinal caeca so distinctive of the genus Perichaeta itself, as contrasted with Megascolex and the other genera, occur, though more numerously, in the African Millsonia, where there are forty or fifty pairs of them. ”

“ The liberated merozoites proceed to infect fresh blood corpuscles and a new endogenous cycle is started.
After asexual multiplication has gone on for some time, sexual forms become developed. According to Schaudinn, the stimulus which determines the production of gametocytes instead of schizonts is the reaction of the host (at the height of a fever period) upon the parasites. A young trophozoite which is becoming a gametocyte is distinguished from one which gives rise to a schizont by its much slower rate of growth, and the absence of any vacuoles in its cytoplasm. ”

“ The worms are tubicolous; "gland-shields" are present on the thoracic segments.
Sub-Order 2. Hermelliformia.—The peristomium (Fig. 135) is enormously developed, and forms a bilobed hood capable of closing over the mouth; the truncated free end of each lobe carries three semicircles of peculiar chaetae, which act as an efficient protection when the worm is withdrawn into its tube. ”

“ Another group of the Condylarthra contains the genus Pertipychus and some others. Periptychus has the full dentition {205}of forty-four teeth, the molars being of course bunodont, with the three chief tubercles most developed. The bones of the tarsus interlock and are not serial, as they are in many other members of the Condylarthra. The astragalus has a shorter neck than in Meniscotherium, for example. It has in this a likeness to the same bone in the Amblypoda, to the primitive members of which, such as Pantolambda, this animal bears much resemblance. ”

“ Specimens of Trichostetha signata are often darkened by diffusion of lipids to the surface after death, particularly visible when fresh adults are pinned.
It is most likely that new undescribed species occur in the least explored mountain ranges, particularly of the Western Cape, as this seems to be the epicenter of the genus, from where radiation presumably occurred in the past. ”

“ Unlike those of alata, somites II and III are not confounded laterally but are distinct throughout. Prostomium short. Tentacles mostly lost in type; rather slender, not long, apparently in but a single transverse series. Peristomium deeply excavated at middle below, the bottom of the excavation rounded and the peristomium produced on each side of this into the usual large lobes. The branchiæ, as in the genotype and other species, strongly asymmetrically developed. The right anterior branchia is much the largest, the trunk very long, with the left anterior much smaller. ”

“ As ancestors of the Artiodactyle section of the Ungulata, we may look to forms more or less closely related to the North American Lower Eocene genera Mioclaenus and Pantolestes, respectively typifying the families Mioclaenidae and Pantolestidae. They were five-toed, bunodont Condylarthra, with a decided approximation to the perissodactyle type in the structure of the feet. A third type of Condylarthra from the North American Lower Eocene is represented by the family Meniscotheriidae, including the genera Meniscotherium and Hyracops. ”

“ The attention of the veterinary profession having been called to the subject of parasitic epizoöty, Mr Lloyd was the first to make search for helminths amongst some few of the carcases of the hundred and more equine animals that perished in South Wales. Two totally distinct epizoötics prevailed. In the Beacons district tapeworms alone were the cause of death, whilst in the Deangunid district scores of animals perished from strongyles. In another district a hundred animals perished from tapeworms. These parasites I identified as examples of Strongylus tetracanthus and Tænia perfoliata. ”

“ But a distinct genus is Perichlamydium, in which the two sieve-plates run on the margin of the lens and form a broad hyaline porous or solid girdle. More important is the distinction of the Ommatodiscida, in which the margin of the disk exhibits one larger osculum, armed with a corona of spines (Ommatodiscus) , or two oscula, opposite on the poles of one axis (Stomatodiscus) . ”

“ This family is one which it is exceedingly difficult to define and to split up into different genera. It shades almost imperceptibly into the Perichaetidae on the one hand, and is very hard to differentiate from the Acanthodrilidae on the other. A Cryptodrilid, like any member of the genus Cryptodrilus, with complete circles of chaetae would be a Perichaetid; and as there are species of Perichaeta in which the anterior segments have only a few chaetae in each segment, it is perhaps wrong to separate the two families at all. ”

“ The Polystomidæ comprise a variety of remarkable genera. I accept this family as the equivalent of Dujardin’s first group of trematodes which he termed “Onchobothriens,” rejecting only his genus Diporpa, which is a juvenile condition of Diplozoon. In this family Van Beneden includes the genera Calceostoma and Gyrodactylus. In all the polystomes we have a more or less ramified intestine, but the reproductive organs conform to the general trematode type. All are hermaphroditic, the eggs being supplied with filamentary appendages, in some only at one pole of the shell, in others at both ends. ”

“ Definition.—Phacodiscida with simple medullary shell, without radial spines, but with a solid equatorial girdle around the margin of the lenticular disk.
The genus Periphæna, founded by Ehrenberg in 1873 for the fossil Periphæna decora of Barbados, differs from its ancestral form Sethodiscus in the development of a very thin siliceous solid girdle around the margin of the lenticular disk; this girdle lies in the equatorial plane of the shell, and reappears in similar form in Perichlamydium among the Porodiscida, in Spongophacus among the Spongodiscida, and in Zonodiscus among the Cenodiscida. ”

“ Of the southern temperate Parastacidae, Australia and Tasmania have the genera Astacopsis and Engaeus; New Zealand 214has Paranephrops, South America Parastacus, and Madagascar Astacoides. The last named genus is rather isolated in its characters, possessing a truncated rostrum and a highly modified branchial system, but it agrees with all the other Parastacine genera, and differs from the Astacidae in the absence of sexual appendages on the first abdominal segment, and in the absence of a distinct lamina on the podobranchiae. ”

“ However, it is now clear that some species are actually associated with different plant species (e.g. Trichostetha coetzeri Holm & Marais, 1988 and Trichostetha fascicularis maraisi Stobbia, 1995) , while others do not seem to feed at all in their adult stage (i.e. Trichostetha dukei Holm & Marais, 1988, Trichostetha hawequas Holm & Perissinotto, 2004, Trichostetha curlei sp. n. and Trichostetha calciventris Stobbia, 1995) .
Several species in this genus have only been described recently, from poorly sampled areas or from isolated mountain peaks ( [4] ) . ”

“ Euprotogonia has been considered to be an ancestor of the Perissodactyle branch, and Protogonodon or Protoselene of the Artiodactyla. If this be true, {200}the likenesses which Titanotherium shows to the Artiodactyla must be either purely superficial and secondary, or a cropping out of ancient characters which had been dormant for many generations.
Horns.—The Ungulata are the only order of mammals which possess horns; as they are on the whole a more defenceless group than the Carnivora, it may be that the horns are a counterpoise to the teeth and claws of the latter ”