12 PnOCEEDIXGS OF THE NATTOXAL MVSEVM. vol. xxvii. 



condition on the last three pairs of legs in Kepon. In Grapsicejpon 

 Giard and Bonnier, the adhesive processes are oval, not wart}'. In 

 Cancricex>un ^^Sky:^ and Bonnier, these processes are riidimentar}-; in 

 Ergyne Risso and Portimicepon Giard and Bonnier, they are strong 

 and muscular. 



^. Marsupiuvi. — The niarsupiuni or brood cavity of the female con- 

 sists on its outer surface of lamelhe or plates affixed to the sides of the 

 segments at the origin of the legs and overlapping on the ventral side 

 in the median line. Sometimes the plates do not completely cover the 

 eggs which are contained in the brood cavity, as in some of the para- 

 sitic Isopoda, the Bopyridw, a large area being left which discloses 

 the eggs. The lamellae or oostegites, which are probabl}" modified 

 epipodites, are usually in pairs of four, one pair for each segment from 

 the first to the fourth, inclusive, or from the second to the fifth, inclu- 

 sive. 



The Cj^mothoidte differ in having five pairs of plates attached to the 

 first five segments and small supplementary plates on the last two 

 segments. The Cirolanida^ also have five pairs of lamellas and supple- 

 mentary ones issuing from the epignath of the maxillipeds. 



In Anthura Leach the incubatory pouch extends over only three 

 segments of the thorax — the third, fourth, and fifth. In AstaciUa 

 Cordiner, Arcturella Sars, Tanais Audouin and Milne Edwards, Psen- 

 <1otaiia!s G. O. Sars, Cryptocope Sars, and Munnopsis auMiYdis Bed- 

 dard, it is confined to a single segment, being formed of only two 

 plates attached to the fourth segment in AstaciUa and Arcturdla and 

 to the fourth free segment, otherwise the fifth segment in the three 

 genera of Tanaidaj mentioned. The Gnathiidfe have no true incu- 

 batory pouch. 



The lamellae in the Epicaridea are usually in pairs of five as in the 

 Cymothoida\ With some genera, as, for example, Phryxus Rathke, 

 those of the two sides are very unequally developed, the plates on one 

 side being much larger than those on the other side. In the Dajidse 

 the brood cavity extends as sacs along the sides of the body. 



The young are retained in the marsupium for some time after they 

 are hatched from the ^^^. 



It has been pointed out that the structure of the incubatory lamellae 

 indicates that they have a respiratory function, and are, to a certain 

 extent, branchial in character, assisting in the oxygenation of the 

 blood. 



D. AliDOMEN. 



The abdomen, pleon or metasome, is typically composed of six seg- 

 ments, five short ones and a large terminal or caudal segment, which 

 comprises the telson. The following modifications occur: The five 

 anterior segments are coalesced with the caudal segment in the super- 



