EMBRYOLOGY AND REPRODUCTION. 



73 



ing as simple uninterrupted layers, and the mesoblast 

 cells remaining stellate : in that case, the epiblast is 



Pig. Ifl. — A, group of larval forms: A, Trochosohere, or larval stage of a 

 worm ; JB, Veliger, or larval stage of a mollusc ; C, Zoea, or larval stage of a 

 crab; D, Caterpillar ("looper''), or larval stage of a moth; B, Tadpole, or 

 larval stage ol: a frog. J) is of natural size, B aliglitly enlarged, and tbe others 

 are represented as considerably magnified. 



known as ectoderm, the hypoblast as eudoderm, 

 ■while the mesoblast is called mesoderm. In some 

 cases the middle layer is called m.eseuchyme, by 



