CHAP. XXXVII.] ' SPERMATOZOON. 549 



That the spermatozoon is really the essential part of the semen, 

 and is that on which all the mysterious fecundating power resides, 

 may be now looked upon as proved beyond a doubt. The latter 

 beautiful observations upon the ova of the frog, of our lamented 

 friend Mr. Newport, have shown that impregnation does not take 

 place unless the spermatozoon actually passes through the vitelline 

 membrane and conies into immediate contact with the yolk 

 substance. 



The chemical analysis of the semen has not yet led to any im- 

 portant results. The investigations of Frerichs are some of the latest 

 that have been undertaken upon this subject. The most important 

 fact which he has established is, that the spermatozoa consist of bin- 

 oxide of protein, the substance of which epithelial cells are chiefly 

 composed. The other constituents of semen are phosphate of lime, 

 fatty matter, a small quantity of extractive matter with alkaline 

 sulphates and phosphates, and a small quantity of phosphorus in 

 an unoxidized state. The imperfectly developed semen contains 

 albumen, but this substance cannot be detected in the fully formed 

 secretion. 



From the various phenomena which we have been considering, 

 and from many other facts which might have been brought forward, 

 we are led to conclude that the spermatozoon is to be regarded in 

 the light of an epithelial cell, or, rather, its nucleus, modified in 

 structure and endowed with peculiar properties. Its mode of de- 

 velopment, the continuous and obviously involuntary nature of 

 the movements, and lastly, its chemical characters, all tend to 

 this conclusion, while they place the originally received notion 

 of the animal nature of the spermatozoon without the bounds of 

 speculation. 



Upon the nature of the force which is communicated by the 

 spermatozoon to the ovum, we know nothing. Whether it is to be 

 looked upon as a catalytic action, or whether the changes induced 

 are of a chemical nature, are questions to which we can give no 

 answer. Certain it is, that the integrity of the spermatozoon is 

 necessary for fecundation. The spermatozoa of hybrids have been 

 found, upon examination, to exhibit structural imperfections, and 

 it has long been known that these animals are incapable of pro- 

 ducing offspring. 



That all the wonderful changes taking place in the ovum, which 

 lead to the formation of the embryo and the development of the 

 new being, result from the agency of the spermatozoon, is certain ; 



