ISOPODA. 



459 



are the first formed. After these have made their appearance, a new 

 cuticle, the larval skin corresponding to the Nauplius stage, is formed 

 (as also is the case in Ligia according to Fr. Miiller). While the 

 other appendages are successively developed, the caudal region of the 

 embryo becomes bent towards the dorsal surface. Of the embryonic 

 membranes the chorion is the first to disappear, then the cuticle of 

 the blastoderm, and finally, when the embryo is fully developed, the 

 Nauplius skin. 



The young animals, when they become free in the brood-chamber 

 (fig. 361), are still without the last pair of thoracic legs; in the 

 Tanaidce the abdominal feet are also wanting. They undergo not 

 inconsiderable changes in the form of the appendages until the 

 attainment of sexual maturity. 

 The Isopoda may therefore be 

 said to undergo a metamorphosis 

 which is most complete in Ta- 

 nais, Praniza (Anceus) and the 

 Bopyridas. 



The Isopoda live some in the 

 sea, some in fresh waters, and 

 some on land (Onisddce). They 

 nourish themselves on animal 

 matters ; many of them are para- 

 sitic (seldom complete endopara- 

 sites, Entoniscus) principally on 

 the skin and in the buccal and 

 branchial cavities of fishes (Cy- 

 ynothoidce) or in the branchial 

 cavity of prawns (Bopyridce). 



Tribe 1. Anisopoda.* 



Body more or less resembling that of an AmpJiipod. The abdomen 

 with biramous swimming feet (Tanais), which do not function as gills, 

 or with Jin-like feet (Anceus). 



Fam. Tanaidae. Tannis (lulhis Kr., Brazil. Two kinds of male?, " smellers 

 and claspers." T. graclUs Kr., Spitzbergen. 



Fam. Pranizidae, Anceida?. Ancuits ma.c'dlaris Mont. (Pr. cairuleata 

 Dcsm.), North and West coasts of Europe. 



* Compare Spcnce Bate, "On Praniza and Anceus, etc," Ann. of Nat. Hint.. 

 Ser. 3, \ 7 ol. II., 18o8. Hesse, ' Memoire sur Ics Pranizes et les Ancdes.'' 

 Ann. (?. Scien. Nat., Scr. IV., Tom IX., 1SG4. Fr. Miiller, " Uebcr den Ban der 

 Scheerenasseln," ArcJiir. fur NatHrgcsdi, Tom XXX., 1864. A. Dohrn, 

 " Entwickelung und Ortranisation von Praniza maxillaris sowie zur KcTintniss 

 des Baues von Paranthura costa,u&"'Zeitschr. fur wi.. Znol., Tom. XX., 1870. 



Fis. 361. Larva of Bopyrui virbii, -with sis 

 pairs of thoracic lefrs (after R. Walz)- 

 VI, Under lip ; Al, ttrst abflominal seg- 

 ment ; A!, A", two pairs of antenna; ; 

 mandible. 



