AMPHIPODA. 



451 



organ. Appendages of the leg> may also be present as additional 

 aids to copulation. The mature ova are, as a rule, carried about by 

 the female in brood pouches formed by the lamellar appendages of 

 the thoracic feet (oosteyites}. Development as a rule takes place 

 without metamorphosis, but the form and appendages of the young 

 animal not unfrequently differ from those of the adult animal 

 (Phronima). The segments and the appendages may even, be incom- 

 plete in number after birth (Isopoda). 



Fossil Arthrostraca are found in the Oolite (Archceoniscus). Pro- 

 soponisci's occurs in the Permian, Amphipeltis in the Devonian. 



1. Sub-order. Amphipoda.* 



Arthrostraca v:ith laterally compressed bod//, with gills on the 

 thoracic feet and an elongated abdomen, of which the three anterior 

 segments bear the 

 swimming feet, while 

 the three posterior 

 bear posteriori// di- 

 rected feet adapted for 

 sjtriitt/iit;/ (fig. 356). 



The .1 i/tph ipoda 

 are small animals, 

 being only in rare 

 case> several inches 

 long (Lysianassa 

 magellanica). They 

 move in the water 

 principally by spring- 

 ing and by swim- 

 ming. The head, which is sometimes small (Crevettina, fig. 356), 

 sometimes large and then much swollen (Hyperina, fig. 357). is 

 sharply distinct from the thorax and is fused with the first of the 

 seven thoracic segments only in the aberrant group of the Lcemod ipoda. 



The two pairs of antenna? usually consist of a short strong shaft 



* Besides the older works of. De Geer. Riisel, M. Edwards, etc.. compare C. 

 Speuce Bate, ' On the Morphology of some Amphipoda of the Division Hyper- 

 ina," Ann. of Xaf. Hist.. Ser. 2. vol. xix.. 1857. C. Spence Bate. On the 

 uidincation of Crustacea," Ann. of Nut. H/xt., Ser. 3. vol. i. C. Spence P.atc, 

 " Catalogue of the specimens of Amphipodous Crustacea in the collect i>n of the 

 British Museum." London. 1802. E. van Beneden et Em Bessels. ' Memoire 

 sur la formation du Blastoderme chez les .Amphipod.es, etc," Bruxelles. 1868. 

 C. Glaus. ' Der Organismus cler Phronimiden, Ai-britr/t tin-, dcm 

 iliT IJniri-rx'ititt Wien, Tom II.. 1*7'.'. 



FIG. 356. Onmmai-1/n m-iilectus (after G. O. Sars), with eggs 

 between the brood lamella? (oostegites) on the thorax. 

 A', A", the two antenna? ; Kf, maxilliped ; F 1 to F~, the 

 seven pairs of thoracic appendages ; Sf, the first swim- 

 mins; foot of the abdomen. 



