Pygidium

“ The mid-region of the body, composed of jointed segments, is followed by a larger or smaller region consisting of fused segments and termed the pygidium or caudal shield, which in some cases is as large as the head-shield itself, in other cases much smaller. When the pygidium is large and composed of many segments, the number of free body segments is correspondingly reduced, and vice versa. It is with respect to this number of segments that respectively constitute the pygidium and the mid-region of the body that Trilobites differ most markedly from each other ”

“ As expected, there are five pairs on the pygidium. The cephalon is unfortunately so exfoliated that the appendifers there are not preserved. The doublure of the pygidium is extremely narrow.
The cast of the interior shows, rather faintly, the exopodites of the right side of the thorax and of the left side of the cephalon, and, still more faintly, the caudal rami and a few pygidial endopodites. The exopodites on the right side are in what seems to be the customary position, directed obliquely forward and outward, and the tips of their distal lobes project slightly beyond the edge of the test. ”

“ The average for the nineteen genera is 13.9 segments in the thorax, 3.7 segments in the pygidium, or a total average of 17.6 segments in the trunk. Crepicephalus with 12-14 segments in the thorax and 4-6 in the pygidium, and Protypus, with 13 in the thorax and 4-6 in the pygidium, are the only genera which approach the average. All of the Mesonacidæ, except one, Olenelloides, have far more thoracic and fewer pygidial segments than the average, while the reverse is true of the Eodiscidæ, Vanuxemella, Corynexochus, Bathyuriscus, and Poliella. ”

“ Photographs of Triarthrus becki, made by C. E. Beecher.
Fig. 1. Specimen 209. Photograph of the pygidium shown in pl. 6, fig. 2. This specimen shows especially well the way in which the exopodites of the pygidium decrease in length backward, × 11.5. ”

“ They are marked by five or six broad furrows and rather broad, flattened ridges that are the continuation on the pleural lobe of the transverse rings on the axial lobe; the posterior margin curves more or less inward toward the median line so as to give a more or less indented outline to the otherwise rounded curve of the sides and posterior margin of the pygidium.
Surface under a strong lens shows numerous pits or pores ”

“ About this same time the Copepoda may have split off [142] from the Hypoparia, continuing in the pelagic habitat. At first, most of the trilobites seem to have led a crawling existence, but about Middle Cambrian time they began to go back partially to the ancestral swimming habits, and retained some of the trunk segments to form a larger pygidium. The functional importance of the pygidium explains why it can not be used successfully in making major divisions in classification. Nearly related trilobites may be adapted to diverse methods of life. ”

“ This might be a very plausible explanation in the case of the bivalve-like Agnostidæ, and it is one I had suggested tentatively for that family before I read Staff and Reck's paper. In the case of the large trilobites with more segments, however, it would be more natural to think of a mode of progression in which there was an undulatory movement of the body and the pygidium, up-and-down strokes being produced by alternately contracting the dorsal and ventral muscles. Bending the pygidium down would tend to pull the animal backward, while bringing it back into position would push it forward. ”

“ The number and character of the bristles of the joints of the legs are used for distinguishing species.
{{smaller|The abdomen is composed of ten segments; on the ninth the tergum is in a great part occupied by a pitted sensory plate called the pygidium. In the male the sides of the tergum form large claspers. A large bristle or bristles project over and beyond the pygidium on the seventh segment, and are known as antepygidial bristles. There is a large and complex penis.
The female flea is larger than the male. The curved receptaculum seminis is a conspicuous object in the female. ”

“ Antennae often long, not elbowed, the first joint not very long. Third joint of tarsus small, usually much concealed by being embraced by the second joint. Pygidium exposed; propygidium deeply grooved in the middle. This family includes 800 or more species, which are mostly tropical; it is very sparsely represented in the faunas of Europe and North America. It is quite distinct from Curculionidae with which it was formerly associated. It contains many graceful Insects having a certain resemblance with Longicorns on account of the large development of the antennae. ”

“ It has also been pointed out that in Naraoia there is preserved down to Middle Cambrian times an animal like that to which ontogeny points as a possible ancestor of the trilobites. Naraoia is not the simplest conceivable animal of its own type, however, for it has built up a pygidium of fourteen or fifteen somites. One would expect to find in Proterozoic sediments remains of similar animals with pygidia composed of only one or two somites, with five pairs of appendages on the cephalon, one or two pairs on the pygidium, a ventral mouth, and a short hypostoma. ”

“ Antliata: insects with a sucking mouth; originally applied to Lepidoptera and Diptera, later and more specifically to Diptera.
Antrorse -sum: directed toward the front.
Anus: the end of the digestive tract, through which the food remnants are passed: the posterior part of the individual: specifically, in Coccidae, a more or less circular opening on the dorsal surface of the pygidium, varying in location as regards the circumgenital gland orifices: = anal orifice. ”

“ Surface slightly roughened, but not pitted or punctate so far as can be determined. The outer half of each pleura is marked by imbricating lines subparallel to the margins of the pleura. Similar lines also occur on the flattened border subparallel to the margin of the pygidium. ”

“ Conocephalidae (Conocoryphidae) (Fig. 150, E) .—The cephalic shield is semicircular, and larger than the pygidium. The glabella narrows in front. The facial suture passes from near the genal angle on the posterior border to the antero-lateral margin, and limits a large fixed cheek and a narrow free cheek. Eyes are absent or rudimentary, but an eye-line is usually present. The thorax consists of from fourteen to seventeen segments with grooved pleurae, which may be pointed, but are not usually produced into spines. The pygidium is small, and formed of few segments. Cambrian. ”

“ If the large pygidium is primitive, then multisegmentation in trilobites can not be primitive but is the result of adaptation to a crawling life. It is annelid-like, but is not in itself to be relied upon as showing relationship to the Chætopoda. Simple trilobites with few segments, like the Agnostidæ, Eodiscidæ etc., were, therefore, properly placed by Beecher at [139] the base of his classification, and there is now less chance than ever that they can be called degenerate animals. ”

“ A high-speed, erratic motion which could be produced by the sudden flap of a pygidium would be of more service in escape than any amount of steady swiftness produced by the oar-like appendages of an animal of the shape of a trilobite. ”

“ The eight genera of the Mesonacidæ, Nevadia, Mesonacis, Elliptocephala, Callavia, Holmia, Wanneria, Pædeumias, and Olenelloides, have an average of 20.25 segments in the thorax and 1.5 in the pygidium, a total of 21.75. ”

“ At any rate, the time of the great development of the straight cephalopods coincided with the time of greatest development of caudalization; both were initiated in the Pacific realm, and both spread throughout the marine world during the middle Ordovician. And since, in the asaphids, a decrease in swimming power of the appendages accompanied the increase in the size of the pygidium, it seems probable that the swimming function of the one had been transferred to the other. ”

“ In the lobster, where this method of progression is most highly developed, there is a large mass of muscular tissue which nearly fills the posterior segments. Trilobites have not usually been thought of as powerfully muscled, but it may be noted that in many cases broad axial lobes accompany large pygidia. As the chief digestive region appears to have been at the anterior end, and other organs are not largely developed, it seems probable that the great enlargement of the axial lobe was to accommodate the increased muscles necessary to properly operate the pygidium. ”

“ The male of Ateuchus stridulates to encourage the female in her work, and from distress when she is removed. (Darwin.) e. Friction of the edge of the elytra against the femur (Chiasognathus grantii) . f. Pygidium with two rasps in the middle (Crioceris, Lema, Copris, Oryctes, Necrophorus, Tenebrionidæ) . g. Abdomen with a grating ridge and four grating plates (Trox) . h. Abdomen with two toothed ridges rubbing on a rasp on edge of wing-cover (Elaphus, Blethisa, Cychrus) . ”

“ It is possible to make out remains of eight pairs of appendages on the thorax, some of them represented by coxopodites only, but most with more or less poorly preserved endopodites as well. No exopodites are visible. The coxopodites of the thorax seem to be of the same form as the last one on the cephalon, but slightly less curved. All are long and heavy, and there seems to be no decrease in size toward the pygidium. The endopodites are very imperfectly shown. ”

“ Observations.—This subgenus is characterized by a nearly smooth surface on the glabella and fixed cheeks, rather large palpebral lobes, and narrow postero-lateral limbs. Unfortunately, no entire specimens of the cephalon and thorax are known, and the pygidia referred to it may or may not belong to the species to which they are tentatively assigned. Only when a thorough study is made of all the material within the Conocephalinæ will it be possible to make even a fairly adequate grouping of the species. ”

“ This is the place where the Pygmies are; this is no fable, saith Aristotle, as 'tis that they are a Dwarfish Race of Men; that they speak the Indian Language; that they are excellent Archers; that they are very Just; and abundance of other Things that are fabulously reported of them; and because he thought them Fables, he does not take the least notice of them, but only saith, This is no Fable, but a Truth, that about the Lakes of Nile such Animals, as are called Pygmies, do live. ”

“ Among the spores are numerous barren filaments or paraphyses.
Puccin ́ia gram ́inis (Pl. VII. fig. 16) is to be found everywhere upon damp rotting straw, and upon grasses. It forms sooty irregular streaks, consisting of densely crowded, one-partitioned (uniseptate) spores (fig. 17) , which appear brown under the microscope. This Fungus is sometimes called “mildew.” There are numerous other species of Puccinia which occur upon common plants.{102}
Urédo seg ́etum is the “smut” of wheat, barley, and oats—a fungus too well known to the farmer. ”

“ In the Pucciniæi the distinctive features of the genera are based upon the more or less complex nature of the pseudospores, which are bilocular in Puccinia, trilocular in Triphragmium, multilocular in Phragmidium, &c. In the curious genus Podisoma the septate [128] pseudospores are involved in a gelatinous element. The diffusion of these fruits is more or less complete according to their compact or pulverulent nature. In some species of Puccinia the sori are so compact that they remain attached to the leaves long after they are dead and fallen. ”

“ The peridium is composed of two distinct layers, one called the cortex, the other the peridium proper. The plant is generally sessile, sometimes more or less stemmed, at maturity filled with a dusty mass of spores and thread.
It affords many of our most delicious fungus food products. The following genera are considered here:
Calvatia—The large puffball. Lycoperdon—The small puffball. Bovista—The tumbling puffball. Geaster—Earth Star. Scleroderma—The hard puffball. Calvatia. Fr.
This genus represents the largest sized puffballs. They have a thick cord-like mycelium rooting from the base. ”

“ For a long time it was believed that Uredo linearis and Puccinia graminis were so many distinct species, but it is now known that there are only three successive phases of the developmental stages of a single species—that, as a matter of fact, puccinia presents the phenomenon of alternation of generations, that is, that the complete development of the fungus is only effected by its transference from one plant to another. ”

“ Very many species of Puccinia have already been found associated with a corresponding Trichobasis, and of Phragmidium with a relative Lecythea, but it may be open to grave doubt whether some of the very many species associated by authors are not so classed upon suspicion rather than observation. We are ready to admit that the evidence is strong in favour of the dimorphism of a large number of species—it may be in all, but this awaits proof, or substantial presumption on good grounds. ”

“ One leaf of the Pinguicula had caught ten of the little leaves of the Erica; and three leaves on the same plant had each caught a seed. Seeds subjected to the action of the secretion are sometimes killed, or the seedlings injured. We may, therefore, conclude that Pinguicula vulgaris, with its small roots, is not only supported to a large extent by the extraordinary number of insects which it habitually captures, but likewise draws some nourishment from the pollen, leaves, and seeds of other plants which often adhere to its leaves. ”