Dr. H. Woodward—On a Fossil Schizopod Crustacean. 403 
Dr. W. T. Calman, of the British Museum (Natural History), who 
has devoted himself for many years to the study of the Crustacea, 
has given special attention to these structures, and finds in them 
a valuable aid to the classification of the Crustacea. In a paper 
published in 1904! he wrote as follows (p. 150 op. cit.) :—‘‘ Among 
the characters in which the Mysidacea differ from the Euphausiacea 
and agree with the Edriophthalmate orders, the most conspicuous is 
the possession by the female sex of a brood-pouch, or marsupium, in 
which the eggs and young are carried. It cannot be doubted that 
this structure is homologous throughout the whole series which 
I have named from this feature, the Peracarida,” in spite of real or 
alleged differences in the mode of its development. It is formed by 
a series of overlapping plates (which Claus considers with great 
probability to be of the nature of epipodites) attached to the inner 
side of the coxopodites of some or all of the thoracic limbs. 
‘‘ When, as in many Isopoda, the coxopodites are fused with the 
body, the plates are attached to the sternal surface of the somites. 
In some cases these plates (or ‘ oostegites’) develop as bud-like 
outgrowths from the bases of the limbs, increasing in size at 
successive ecdyses as sexual maturity is approached; but in certain 
Isopoda it has been shown that the course of development is abbre- 
viated, the ‘oostegites’ growing in the space between the sternal 
cuticle and the hypodermis, and being set free completely formed 
at a single moult.’’’ 
‘Probably some similar process has given rise to the statement 
that the oostegites arise by splitting of the ventral cuticle in the 
Cumacea‘ and in the Isopod Gnathia® At the same time it is 
certain that the formation of the brood-pouch is profoundly modified 
in certain parasitic Isopods of the tribe Epicaridea. In many of 
these the ‘oostegites’ develop in the typical fashion just described, 
but in the more specialized forms the structure is very different 
and hard to understand. 
“In Hemioniscus, where the development has been worked out in 
detail by Caullery & Mesnil,* the marsupial cavity is hollowed out 
in a thickening of the ectoderm on the sternal surface, and is from 
the first completely closed. Further research will be required to 
show what relation this cavity bears to the normal marsupium.”’ 
‘Apart from such exceptional cases, however, the possession of 
oostegites is a character quite peculiar to the group of orders included 
in the Peracarida and not found in any other Crustacea. It is true 
that the Kuphausiidz are described as carrying their eggs in sacs 
attached to the sternal surface of the thorax, and it has been assumed 
1 «On the Classification of the Crustacea Malacostraca,’’ by W. T. Calman, 
D.Se.: Ann. & Mag. Nat. Hist., ser. vir, vol. xiii (1904), pp. 144-158. 
2 From mypa, pera, a pouch, and carida, a shrimp. 
3 Cf. Leichmann, ‘‘ Beitr. z. Naturgesch. d. Isopoden”’: Bibl. Zool., x (1891). 
4G. O. Sars, ‘‘ Beskr. af de paa Freg. Josephines Exp. fundne Cumaceer’’ : 
Kongl. Svenska Vet.-Akad. Handl., ix, 13 (1871), p. 19. 
5 Dohrn, ‘‘Entw. und Organ. v. Praniza (Anceus) mazillaris” : Zeitsch. f. wiss, 
Zool., xx (1870), p. 70. 
6 <* Recherches sur 1’ Hemioniseus balani, Buchholz . ... ”: Bull. Sci. 
France et Belgique, xxxiv (1901), pp. 316-362, pls. xvii, xviii, 5 figs. in text. 
