70 AN INTRODUCTION TO ZOOLOGY. 



is called Segmentation ; the product is called tbe 

 Morula, or mulberry stage, because it is like a 

 mulberry in shape. It has been shown compara- 

 tively lately, that each of the " segments " of the 

 morula is an amcebiform cell, connected with the 

 others by means of pseudopodia. In order to express 



Fig. IB. — Developing ovum of a starfisb : a, with four segments ; b, "with 

 eight. — (From Glaus and Sedgwick, after A. Agassiz.) 



this interconnection of the cells, the name Syncytium 

 has therefore been given to this stage. It is believed 

 that the cells and tissues in adult animals are for the 

 most part similarly connected. Very frequently a 

 round ball, hollow in the middle, is formed instead of 

 a round bunch, the cells forming a thin layer round 

 the hollow. This is called the Blastosphere or 

 Blastula. 



Tlie next stage is called the Gastrula, or Stomach- 

 animal; it is formed by the flattening and curving in 

 of one end of the sphere, until there is a little bag 

 inside the sphere at that end. The little bag repre- 

 sents the primitive stomach; it is called the Arch.- 

 enteron, or primitive internal cavity: the mouth 

 which leads to it is believed to represent the primitive 



