PRESENT STATUS OF CHONDRIOSOME PROBLEM. 77 



the small amount of protoplasmic ground-substance which, in 

 the mammalian spermatozoon, forms a thin covering over the 

 head and the proximal part of the tail. But there is another 

 constituent which the recent studies have shown to be constant 

 in all spermatozoa of all species, from the lowest to the highest 

 groups. These are the chondriosomes. The same studies have 

 shown also that the chondriosomes can assume in the ripe 

 spermatozoon a shape and location which vary greatly in the 

 different species. One used to say that the chondriosomes form 

 a sheath around the "middle-piece" of the spermatozoon. This 

 is a very loose, and in many cases an entirely incorrect statement. 

 Loose, since under the term "middle-piece" we designate parts 

 that have nothing in common : there is no homology whatsoever 

 between the so-called "middle-piece" of the spermatozoon of an 

 echinoderm, of a selachian (or an amphibian) and of a mammal. 

 In many cases it is also an incorrect statement. In a number of 

 higher vertebrates, especially in mammals, the chondriosomes 

 actually form a sheath around what is customarily called the 

 "middle-piece" of the spermatozoon; at the same time, the shape 

 of that sheath varies a good deal, from isolated granules to discs 

 or a spiral filament. In lower vertebrates (in many fishes) and 

 in a great number of invertebrates (many molluscs, certain 

 worms, etc.), the chondriosomes are represented by a small 

 number of granules located on the posterior part of the head and 

 surrounding the origin of the tail. A third type often met with, 

 especially in insects, is represented by a long, thin sheath, which 

 envelops the axile filament; this sheath is derived from the so- 

 called "Nebenkern," which usually breaks in two, the pieces 

 afterwards becoming elongated as the tail grows. But besides 

 these three main types there exists also an infinity of other 

 forms. Quoting at random I would mention the spermatozoa of 

 Ascaris, Phallusia, Ciona, of many worms, Crustacea, molluscs, 

 etc. It is consequently impossible, in the presence of the ripe 

 spermatozoon only, to decide what part of it is formed by the 

 chondriosomes 1 and only a careful study of spermiogenesis can 

 solve the problem. Indeed such a study should be undertaken 



1 This is a reason why I cannot, without further investigation, consider F. R. 

 Lillie's observations on fertilization in Nereis as demonstrating that in that species 

 the male chondriosomes do not penetrate into the egg. 



