10 Hjalmar Théel, 



The radiation of pseudopodia into the intermediate space of 

 normal or abnormal eggs is of course only transitory and vanishes 

 before the appearance of the phenomena of segmentation. As to the 

 origin of the pseudopodia, it appears to be in close connection with 

 the gradual separation of the vitelline membrane, their free ends being 

 attached to the membrane, thus constituting a series of threads, which 

 cross the still increasing intermediate space. An examination of eggs 

 with large, abnormal, easily distinguishable processes convinces one that 

 the process takes place in the way above mentioned. 



Before finishing this chapter I may as well draw attention to a 

 certain difference between the fertilized eggs of Echinocyamus and those 

 of Toxopneustes variegatus described by Selenka '). He says that the 

 vitelline membrane is scarcely removed from the outmost layer of the 

 yolk, before the mucilaginous investment begins to dissolve, and that 

 after five minutes no trace of it is to be detected. This is by no 

 means the case in Echinocyamus, because here it; remains as a true 

 envelope during almost the whole process of segmentation, and in cer- 

 tain cases it also surrounds the young Blastula. But it becomes glassy 

 and transparent in such a high degree, that it is scarcely to be per- 

 ceived without reflecting on it different lights by the mirror of the 

 microscope or placing the eggs in some colouring fluid. Possibly the 

 envelope in question serves for defence during the time when the em- 

 bryo lacks the power of free movement. 



With regard to the remaining phenomena which are in connection 

 with the act of maturation and fertilization, I have nothing of im- 

 portance to add to what is already known. As soon as the head 

 of the spermatozoon enters the vitellus and is transformed into the 

 »male pronucleus», it rapidly increases in size and passes from the 

 periphery towards the centre of the egg in order to meet the »female 

 pronucleus». This, which at first seems almost motionless, starts to 

 meet it and finally fuses with it, the two nuclei forming together 

 a new nucleus, »the first segmentation nucleus», which is completed 

 after about ten minutes from the beginning of the impregnation. The 

 protoplasm, which was first arranged in radiating lines round the »male 

 pronucleus» during its passage from the periphery, now forms round 



1) Zoologische Studien. I. Befruchtung des Eies von Toxopneustes variegatus. 

 Mit drei Tafeln. Leipzig 1878. p. 7. 



