32 COMPARATIVE ANATOMY AND PHYSIOLOGY. 



' by the male element (chap. xiii. ), and then commences 

 to undergo a process of cleavage, or division. It first 

 divides into two cells, which are, in the simplest cases, 

 equal in size ; each of these again divides, so that there 



Fig. 5. Segmentation of AmpUioxus. 



A, Stage with two equal segments; B, with four; c, with eight; r, segments 

 enclosing a segmentation cavity ; E, somewhat older stage in optical section. 

 (After Kowalevsky.) 



are four, then eight, and so on. After a time the pro- 

 cess of segmentation (Fig. 5) comes to an end, and 

 then we have a mass of segments, which are either 

 closely applied to one another, and so have a kind of 

 mulberry-like appearance (hence the name of inorula 

 applied to this stage) ; or, as is more common, the 

 segments separate from one another during the 

 process of division, and give rise within to a space, 



