STAGE A. 3C Hours old. 

 At the age or thirty siz hours the larvae, swim 

 actively, they being uniformly covered with cilia 



Fig.l. 



The shape of the larvae is an oval, the length 

 being to the shorter diameter as 2 is to 1. 



The animal or anterior pole is sleightly 

 pointed than the posterior vegitative one. The ven- 

 tral surface is distinguished by the presence of the 

 blastopore v:hich latter has been pushed from its 

 posterior position to a ventral one by the rapi ■ 

 growth of the sctoderm of the dorsal surface of the 

 larva. . 



An apical plate of taller cells is present at 

 the anterior snd but I could not see that the cilia 

 at this point were any longer than those which cover 

 the other part- of the larva, "ty. 3. *£ 



From ths blastopore , through which its cavity 

 opens to the exterior, a large archenteron projects 



j.rd into the blastccoele. 



The remainder of the blastocoele ,not taken up 

 by the archenteron or its pouches, is filled with a 

 close net-work of mesenchyme cells. This mesenchyme 

 tissue is shown in Fig, 3, which is a longitudinal 

 sagittal section of "A", 



