2_}2 NEIL S. DUNGAY. 



been called forth within the egg. The achromatic parts of the 

 mitotic figure are entirely absent although there are indications 

 that the chromosomes may undergo a part of the changes pre- 

 liminary to first cleavage The effects produced by the attach- 

 ment of the sperm seem to be nearly the same as those secured by 

 centrifuging the eggs or by giving them any mechanical stimulus 

 (Lillie, 'n). 



It is of interest to find that a few of the eggs of the type 

 described above show the presence of two or more sperm cells 

 attached to the vitelline membrane. This has been found in 

 several cultures in which many eggs showed no evidence of having 

 come in contact with a sperm cell. Apparently the weakened 

 sperm cells are not able to promptly call forth in the egg the 

 reaction which prevents the attachment of more than one sperm. 

 The partial jelly formation which was observed in the living 

 material is often associated with the failure of the sperm to enter 

 the egg. However cases have been seen in which the sperm 

 entered and caused first cleavage to take place. The farther 

 history is not known but, since preservations made from some- 

 what later stages show no traces of such eggs, it is probable that 

 the cortical alveoli are soon. emptied. 



(b i) A very interesting observation upon the living material 

 has been recorded above. In many experiments a few eggs 

 seemed to have nearly completed the process of first cleavage 

 when the cleavage plane ceased to advance and gradually faded 

 away. Cytological examination fails to pick out these eggs until 

 the early telophase stages of first cleavage. The earlier processes 

 seem to go on in a normal manner. In most cases the chromo- 

 somal vesicles fail to unite properly and the plane of cleavage 

 fades away. Usually it leaves behind a change in the arrange- 

 ment of the yolk granules and its position is occupied by a some- 

 what lighter staining band in which small granules are less abun- 

 dant. Parts of the sharp line which marks the completed cleavage 

 plane in sections may be left behind, especially those parts near 

 the animal pole of the egg (Fig. 8). The chromosomal vesicles 

 sometimes scatter widely and partially dissolve and sometimes 

 they remain near each other. Very often the region near the 

 vesicles becomes filled with deeply stainirg granules. In one case 



