EFFECTS OF INJURY UPON SPERM. 219 



portion of eggs with jelly varies considerably among different 

 lots, so much so that an occasional batch of eggs is found in 

 which the majority form jelly. This jelly formation is probably 

 not due to accidental insemination since fertilization cones are 

 not seen and cleavage does not result. Yet to guard against 

 possible misinterpretation an unfertilized control was kept for 

 each experiment and examined along w T ith the experimental 

 materials. 



The active spermatozoon may be seen to attach itself to the 

 egg. It immediately becomes quiescent and remains motionless 

 until it is drawn into the egg. The outflow of jelly, which con- 

 tinues for some fifteen minutes after insemination, now sweeps 

 away all superfluous sperm cells, which have in the meantime 

 lost their power of motion. Just beneath the attached sperm 

 cell an attraction cone is pushed up by the egg cytoplasm until 

 it unites with the membrane. It then gradually disappears, 

 carrying with it the membrane so as to form a depression in 

 which the sperm is now concealed. This all happens during the 

 first 25 minutes after insemination. In the meantime the 

 germinal vesicle has disappeared and the egg has assumed an 

 irregular shape. About 45 minutes after insemination the egg 

 resumes its spherical form and soon the sperm, after again coming 

 prominently into view r for a short time, is drawn into the egg. 

 Shortly before the close of the first hour succeeding insemination 

 the first polar body appears and is followed in a few minutes by 

 the second. The polar bodies are easily seen at this time against 

 the now yolk-free region of the pole. In a profile view they are 

 very conspicuous. In the course of the second hour the first 

 two planes of cleavage appear. The first plane, as has been 

 stated by Just ('12), passes through the point of entrance of the 

 sperm, dividing the egg unequally. The development proceeds 

 rapidly from this point. Movement is often seen in twelve 

 hours and fine trochophores are formed by the end of the first 

 day. In the second day the animal begins to elongate and the 

 larval setae grow out to a relatively great length. Naturally 

 the time element, as given above, varies greatly with the tem- 

 perature. 



