Didymus

“ But Apion and Diodorus say, "There are some kinds of phialæ of which the boss is similar to a strainer." But Asclepiades the Myrlean, in his Essays on Cratinus, says— "βαλανειόμφαλοι are the phialæ called, because their bosses and the vaulted roofs of the baths are much alike." And Didymus, saying the same thing, cites the words of Lycophron, which run thus:—"From the bosses in the women's baths, out of which they ladle the water in small cups." ”

“ A.D. 10) , Greek scholar and grammarian, flourished in the time of Cicero and Augustus. His surname (Gr. Χαλκέντερος, brazen-bowelled) came from his indefatigable industry; he was said to have written so many books (more than 3500) that he was unable to recollect their names (βιβλιολάθας) . He lived and taught in Alexandria and Rome, where he became the friend of Varro. He is chiefly important as having introduced Alexandrian learning to the Romans. ”

“ Extinct Didelphyidæ.—No less than seven species of Didelphys have been found in the caves of Brazil, but none in the older formations. In North America the living species only, has been found in Post-Pliocene deposits. In Europe, however, many species of small opossums, now classed as a distinct genus, Peratherium, have been found in various Tertiary deposits from the Upper Miocene to the Upper Eocene. ”

“ If we assume the region of origin and center of dispersal of a group of animals to be the one in which the greatest numbers of the most specialized species of a given genus are found, then the northern Tableland of Mexico and the adjoining region of the United States in southeastern California and southwestern Nevada is the region of origin and the center of dispersal for the genus Dipodomys. Dipodomys deserti, Dipodomys merriami, Dipodomys panamintinus, Dipodomys microps, Dipodomys phillipsii and Dipodomys ordii are found in the region mentioned. ”

“ In an earlier edition this species was entered as P. obrusseum following the Polish text. Miss Lister who has the type of Didymium obrusseum at hand considers it as representing a phase of Physarum polycephalum Schw. D. tenerrimum Berk. & Curt. is judged the same. P. tenerum Rex is, in any event, certain, and the combination is adopted.
Rare:—Pennsylvania, Ohio, Louisiana, Texas, Iowa, Portugal, Japan. ”

“ The head of the Didelphis crassicaudata is shorter and less pointed than in most other Opossums; the ears are unusually small, and the tail is very thick. In the character of the fur also, this species differs from most others, the hairs being rather short and somewhat adpressed; and the soft under fur being very scanty. Upon separating the fur on the back and sides of the body, numerous young hairs were visible in the specimen from which the above description is taken, and these were of a bright rusty red tint ”

“ His conclusion seems to be correct, but actually other species of Proechimys (subgenus Trinomys) , for example, P. dimidiatus, have four or more crests in each cheektooth, and, therefore, may be considered as more closely related to Cercomys than is P. setosus. If a large number of crests indicates primitiveness, P. dimidiatus, always with four, is more primitive than any other species in the subgenus Trinomys. Also, the large skull, long hind foot, short tail and thin aristiforms of P. dimidiatus, in my opinion, are primitive characters. ”

“ Owing to the lack of known intergradation between the three, I judge that they should be retained as full species, but the difference in degree of morphological specialization is no more than would be expected between subspecies. I have examined no specimens of Dipodomys elator but from what I know of its morphology, I think that Grinnell better indicated its relations in allying it with D. phillipsii than did Davis in erecting a new group for it on the basis of linear measurements. ”

“ The genus Didelphys contains most of the forms belonging to this family, including as it does some twenty-three species. The Opossums are mainly arboreal animals, insectivorous in their food; but the larger species eat reptiles, birds, and their eggs. Several of the small species carry their young, when able to leave the teats, on their back, the tails of the young being wrapped round that of the mother. It is not only the pouched species which carry their young in something of this fashion. ”

“ Color dark, entire dorsal surface near Olive-Brown, purest on sides and flanks, upper parts strongly suffused with black; cheeks white; arietiform markings, pinnae of ears, plantar surfaces of hind feet, dorsal and ventral stripes of tail which are wider than white lateral stripes, blackish. Skull small; rostrum relatively short and wide; interorbital region wide; interparietal region wide; foramen magnum elongate dorsoventrally; pterygoid fossae ovoid.
Comparisons.—From Dipodomys ordii utahensis, which it closely resembles, D. o. panguitchensis differs in: Size larger; color darker ”

“ Fig. 45.—A, B, C, Stages in the development of the vermiform larva in Dicyema typus van Ben. (After Ed. van Beneden.) cal, "Calotte"; gc, germinal cell; n, nucleus of endodermal cell.
The animals composing this group are minute and parasitic, and are composed of a small number of cells. They may be divided into two families: the Dicyemidae, which occur exclusively in the kidneys of certain Cephalopods (cuttle-fish) ; and the Orthonectidae, which live in the brittle-star Amphiura squamata, the Nemertine Nemertes lacteus, or the {93}Polyclad Leptoplana tremellaris. ”

“ From Dipodomys ordii fetosus, D. o. pallidus differs in: Size larger; color lighter; ventral stripe of tail indistinct as opposed to pronounced; skull larger; nasals longer and more flared distally; auditory bullae larger; external auditory meatus larger; palate shorter and broader.
For comparisons with Dipodomys ordii marshalli and Dipodomys ordii utahensis see accounts of those subspecies. ”

“ The species Didelphis marsupialis, which is common in the eastern United States and extends through temperate North America, Central America and tropical South America, has a complete pouch and is chiefly arboreal and insectivorous in habit. In the woolly opossums (Caluromys) there is no pouch, and the young, when sufficiently advanced, are carried on the mother’s back, winding their tails around hers. In both of these genera the tail is long, naked and prehensile, but in the tiny species of Peramys the tail is short and hairy. ”

“ Athena, who held Tydeus in special favour, hastened to the field of battle, to heal him of his wound and bestow immortality upon him. But the sight of Tydeus, cleaving open the skull of his dead enemy and sucking out his brains, so disgusted her that she left him to his fate. Tydeus married Deipylē, the daughter of Adrastus, by whom he had a son, the famous Diomedes, frequently called Tydides. ”

“ But go on, Digby, never be ashamed of asking questions, although, now and then, they may bring down a laugh upon you. It would fare but ill with the poor crabs and lobsters if they were not black, or rather of the colour of the rocks and weeds among which they live. Their colour thus enables them to escape detection from the sharp-sighted fish, which are constantly swimming rapidly about in search of them, and, in spite of their coats-of-mail, easily gobble them up. But I was going to show you this little pea-crab, Pinnotheres. ”

“ The specimens mentioned above, along with the information recorded by Davis (loc. cit.) and other authors (for example, J. A. Allen, loc. cit., and Bull. Amer. Mus. Nat. Hist., 16:249-279, August 18, 1902) , give basis for arranging the North American Didelphis as follows:
In listing the subspecific names given immediately above we are aware of the possibility that a thorough study of the geographic variation in Didelphis marsupialis may contract or expand the list of recognizable subspecies. ”

“ With the accumulation of additional material and with the knowledge that certain kinds treated by Grinnell as full species are in actuality subspecies, it is felt that the several species of kangaroo rats can best be arranged in six groups which, from the least to the most specialized, are as follows:
Ordii Group.—Composed of the subspecies of Dipodomys ordii and Dipodomys microps. Grinnell placed these two species in separate groups; Burt on characters of the baculum alone placed D. microps with Dipodomys deserti and Dipodomys spectabilis. ”

“ Drawing from description of the Sieur D.B. (Dubois) , 1674.
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PEZOPHAPS STRICKLAND & MELVILLE.
Skull with a moderate rostrum, slightly hooked, and the nasal and maxillary processes of the praemaxillae diverging anteriorly; the frontal region flat with but little cancellous tissue. Coracoid stout. Manus armed with an ossified tuberosity. Neck and feet long. Delto-pectoral crest of humerus aborted.
This genus connects Didus with the Columbidae. The male is much larger than the female. ”

“ Populations from a given locality are remarkably stable in color except the animals from Samalayuca, Chihuahua, which vary in color from individuals almost as light as D. o. compactus to animals that approach D. o. ordii in darkness of pelage.
The subspecies of D. ordii show no noticeable variation in the extent of the hip stripe, supraorbital and postauricular spots, basal white ring of the tail, lateral stripes of the tail or the extent of white on the venter and feet. There is, however, variation in the degree and extent of the arietiform facial markings. In Dipodomys ordii utahensis, D. o. ”

“ On the anterior limbs all the five digits are provided with long sharp claws, and the first toe is but little opposable. The numerous cheek-teeth are crowned with minute sharply-pointed cusps, with which to crush the insects on which these creatures feed, for the opossums seem to take in South America the place in the economy of nature filled in other countries by hedgehogs, moles, shrews, &c. The true opossums are typically represented by Didelphys marsupialis, a species, with several local races, ranging over the greater part of North America (except the extreme north) . ”

“ The first family is that of the true or American opossums—Didelphyidae, in which there are five pairs of upper incisors, while the feet are of the presumed primitive arboreal type, the hind foot having the four outer toes sub-equal and separate, with the first opposable to them all. With the exception of the water-opossum, forming the genus Chironectes, all the living members of the family may be included in the genus Didelphys. ”

“ As regards geographical distribution, existing marsupials, with the exception of two families, Didelphyidae and Epanorthidae, are mainly limited to the Australian region, forming the chief mammalian fauna of Australia, New Guinea, and some of the adjacent islands. The Didelphyidae are almost exclusively Central and South American, only one or two species ranging into North America. Fossil remains of members of this family have also been found in Europe in strata of the Oligocene period. ”

“ In no cranial feature other than shortened nasals and narrowed rostrum, does Dipodomys ordii show a gradation such that it might be termed a cline. Other parts of the skull that were measured do not vary greatly.
Perhaps the greatest amount of variation in the skull is in features which are not readily measurable by the usual physical means. The shape and size of the pterygoid fossae vary from almost round to rather ovoid in a given series of animals from one locality; the size and configuration of the zygomatic arches vary from slender to robust and from straight to curved laterally ”

“ In the stock isolated in California, however, even though two large species have been formed they are still below the average in degree of specialization for the genus. As noted elsewhere in this paper, the species from these low, hot valleys, excepting D. nitratoides, are all closely related one to another. Dipodomys venustus and Dipodomys elephantinus are either closely related species or possibly only subspecies of one species, Dipodomys agilis.
It is worthy of note that as the distance away from the center of differentiation increases, the number of species decreases. ”