Embryogenesis from the Spermatozoon 305 



of a small amount of some substance having a low refractive 

 index about the middle pieces of some of the spermatozoa. In 

 favorable cases as many as 60 per cent of the spermatozoa may 

 undergo this change. At this time many of these spermatozoa 

 are still swimming. During the course of the next few hours 

 these lowly refractive areas increase in size until they are about 

 half as long as the sperm head and acquire a fairly distinct 

 ellipsoidal outline. Then in many cases the sperm head can 

 be seen to be bent in a horseshoe or spiral shape, and to be 

 included in the wall of the vesicle, which has now become 

 spherical, while the tail of the spermatozoon still remains 

 unchanged or has disappeared without taking any part in the 

 transformation. The next change is an increasing indistinct- 

 ness in the sperm head, and an increasing refractive power of 

 the whole vesicle so that it can hardly be discriminated at all 

 in the albumen. It is not possible to follow the process farther 

 in unstained material. 



In some cases these vesicles instead of being spherical stretch 

 out along the whole side of the sperm head, or may become 

 entirely disconnected from the spermatozoon. 



If yolk is used as a culture medium for the sperm essentially 

 the same phenomena occur; and in the various Ringer solutions 

 vesicles containing the sperm heads are also formed, but in the 

 Ringer solution, as a rule, the steps in the formation of these 

 vesicles could not be seen without staining. 



When the hanging drops are fixed in Flemming's fluid and 

 stained and examined in Herla's vesuvin and malachite-green 

 mixture, it can be seen that in its early stages the vesicle has 

 distinct walls and a homogeneous unstained fluid of a low 

 refractive index in its interior. This fluid is possibly water and 

 this would account for the fact that the vesicle is conspicuous 

 in albumen and yolk, but invisible in Ringer solution. 



The vesicle seems to be formed by the imbibition of water 

 by the very thin protoplasmic envelope of the sperm head and 



