GERMINAL LOCALIZATION IN THE EGG OF CEREBRATULUS. 19 



pilidia were developed. Of these seven were ^destitute of the 

 apical organ and one without the enteron, the remaining nineteen 

 also showed more or less abnormality as had been noted by 

 Wilson ('03 p. 432), the commonest mal- 

 formation being the shifting of the apical 

 organ to one side. An extreme case is 

 shown in Fig. 17. In general appearance 

 the 3-larv8e strikingly resemble young pilidia. 

 Both are provided with a straight gut and 

 a circular ciliated band. The ^-embryo 

 shows in every respect features of arrested development such as 

 were seen, though in less degree, in the ^-pilidia. Why it is so 

 I am not prepared to say. It may be due to a lack of material 

 or to some correlative factor, or more probably to both. The 

 lack of the apical organ in some of the ^-embryo seems to show 

 that the mutual pressure of the blastomeres plays an important 

 rôle in normal embryogeuy. 



Series Q. Isolation Experiment at the 8-cell Stage 

 into 5 Animal and $ Vegetal Cells. 



The upper quartet (4 A) of the 8-cell stage was separated 

 from the lower (4 V). Seven pilidia were produced from the 

 former and three from the latter.^ 



4 A 



5 anenteria (Fig. 18 A, B, C and E). 



1 pilidium with a solid cell mass. (Fig. 18 F). 



1 nearly normal (Fig. 18 D). 



4 It ^lioulil be noted tliat the vegetal larvie are far less teuaccons of life than those 

 from the animal quartet, as in the case of the sea-urcliin egg. 



