232 



ANIMAL BIOLOGY. 



[Part II. 



recognised by two pairs of imperfectly tubular appendages on the 

 under side of the anterior end of the abdomen, pointing for- 

 wards, beneath the unjointed thoracic region. 



A. 



P. 



FIG. 73. CRAYFISH EXOSKELETON. 



A. Dorsal view of crayfish. B. Side view, with appendages removed. 

 C. Diagram of abdominal somite. D. Cross-section of cephalo-thorax. 

 E. Endophragmal system in cross-section. F. The same from above. 



ar. Articular cavity, arth. Arthrophragm. "br. c. g. Branchio-cardiac 

 groove, c. en. st. Capital of endosternite. cv. g. Cervical groove, en. pi. 

 Endopleurite. en. st. Endosternite. ep. Epimeron. h'. p'. Anterior hori- 

 zontal process, h. p. Posterior horizontal process, pi. Pleuron. st. Sternum. 

 te. Tergum. id. Telson. xv.-xx. Abdominal somites. 1-3, 10-14, 20. Appen- 

 dages visible in dorsal aspect. 



External Characters. The body ef the crayfish is easily seen 

 to have the following parts (Fig. 73, A.) : 



1. The Cephalo-thorax, occupying the anterior half of the body. 

 The whole of this region is encased in a continuous shell, the 

 carapace, ending anteriorly in a pointed rostrum. 



