VI 



CLASSIFICATION 



371 



pair ot appendages divisible into podomeres ; in addition 

 to this, there is an ahnost universal absence of cilia in the 

 phylum, the sperms are usually non-motile, the muscles are 

 nearly always of the striped kind, and the body-cavity, which 



Fig. 92. — Early embryo of the Crayfish in the iiaupllLis stage. 

 A ill the upper part of the figure is the eye ; /. the labrum overhanging the mouth, 

 on each side of which are the rudiments of the antennules (a^.), antenna: (a-.), 

 and mandibles (w.) ; behind them is the rudiment of the thora.x and abdomen 

 (TA) with the anus (A). The rudiments of the first three pairs of ganglia 

 ((7. ga'-, gtji,) are seen through the transparent ectoderm. (From Lang, after 

 Keichenbach.) 



does not represent a true ccelome, is largely represented by 

 blood-spaces in free communication with the circulatory 

 system. 



The phylum is divided into several classes, which are all 

 air-breathing except the Crustacea, the class to which the 

 Crayfish belongs and which also includes the Lobsters, 

 Crabs, Shrimps, Wood-lice, Barnacles, Water-fleas, &c. 



B B 2 



