143 



A. 



It was my wish to test as far as possible Boveri's extremely im- 

 portant results on the fertilization of the egg-fragments of Sphaer- 

 echinus with the spermatozoa of Echinus. Some of these fragments 

 produced small larvae, showing in their skeletal structures a condition 

 mid-way between the paternal and maternal form. Other pieces showed 

 only the form peculiar to the paternal larva. Boveri believed the 

 former to have come from the nucleated egg-fragments of Sphaer- 

 echinus, and the latter from the non - nucleated fragments of Sphaer- 

 echinus fertilized each by o n e spermatozoon of Echinus. The evidence 

 for this conclusion rests on the structure of the paternal larval-form 

 and also on the statement that in these paternal larvae the nuclei 

 were only half the size of those of the corresponding stages of the 

 crossed larvae. 



Boveri believes the latter condition is due to the entrance of but 

 a single spermatozoon, so that the first segmentation nucleus would 

 be only half size, and this condition Boveri thinks must be handed 

 down to all of the nuclei that are the descendants of the male nucleus. 

 It seemed that a careful study of the behavior of egg - fragments 

 fertilized with their normal sperm might throw some light on Boveri's 

 results. The eggs of Arbacia were shaken violently for several minutes 

 so that many egg - fragments were produced, some nucleated, others 

 not. Some of the fragments were not surrounded by egg-membranes, 

 while others were. In Arbacia it is impossible to tell from the living 

 egg -fragment whether or not it contains a nucleus. Preparations of 

 hardened and stained eggs must be made. As a rule those fragments 

 that remain surrounded by the egg -membranes develop while those 

 outside only occasionally develop. It seems clear that the fragments 

 remaining in the membrane are in every case nucleated, while only a 

 few of those outside the membrane contain the egg-nuclei. 



Two questions need to be settled. Do the non-nucleated pieces 

 segment and develop? Do the fertilized nucleated egg - fragments 

 produce embryos with nuclei the full normal size? Hertwig saw 

 spermatozoa enter the non - nucleated pieces and there undergo karyo- 

 kinetic division. He thought these fragments did not segment and 

 that they subsequently broke down. Boveri claims that when mono- 

 spermic fertilization of non-nucleated pieces took place, the fragments 

 not only segmented, but formed (paternal) larvae as well. Although 

 I have studied large numbers of egg-fragments, I have never gotten 

 any definite proof that the non - nucleated pieces segmented. That 



