TEE DETERMINATION OF SEX. 107 



kinds of spermatozoa has lost its power of fertilizing the egg and in 

 most cases has become degenerate. 



In respect to the occurrence of the two kinds of spermatozoa, 

 Beard brings together rather a heterogeneous collection of facts. It 

 has been known for some time that in a few cases two kinds of sper- 

 matozoa are found. The oldest and now the most thoroughly studied 

 example is that of the snail, Physa vivipera. In this animal there are 

 hair-like spermatozoa that resemble the ordinary forms of spermatozoa, 

 and also worm-like forms which are as numerous as the other kind. 

 A remarkable fact has recently been discovered by Meves in regard to 

 these spermatozoa. An unusual and probably degenerate process 

 occurs in the formation of the worm-like spermatozoon, so that instead 

 of containing the reduced number (seven) of chromosomes it con- 

 tains but a single one. In another form, Pygcera, this second form 

 of spermatozoon contains no chromatin material whatsoever, i. e., it is 

 headless and presumably functionless as well. 



In the long list of cases given by Beard in which two forms of 

 spermatozoa have been described, there are several cases in which the 

 two distinct forms appear to be always present and characteristic, as in 

 the cases cited above; but he has also included some other cases in 

 which giant spermatozoa occur, and some of these at least have been 

 shown to be the result of a failure of the spermatocytes to divide. 

 Until it can be shown that this failure to divide is usual and charac- 

 teristic of one set of these spermatocyte cells the result may really 

 have no bearing at all on Beard's contention. 



Much more striking are the cases in which there is an accessory 

 chromosome present in two of each of the four cells that develop from 

 a single spermatogonial cell. The discoveries of McClung, Mont- 

 gomery and Sutton in this connection indicate that there are two 

 kinds of spermatozoa, and McClung has urged that this difference is 

 connected with the determination of sex; but there is nothing more 

 than the supposition that this may be so to go upon at present. In 

 these cases, although the form of the spermatozoa is the same for the 

 two kinds, there appears to be a difference in the amount of the 

 chromatin material. It has not been shown that a difference of this 

 kind would have any value in the determination of sex, and even if 

 this were the case the results do not conform to the requirements of 

 Beard's theory, as we shall see presently. 



Beard calls attention to the fact that in nearly all the cases in 

 which two kinds of spermatozoa have been described there is evidence 

 of the degeneration of one of the two kinds. Prom this he draws the 

 rather sweeping conclusion that throughout the animal kingdom one 

 of the two forms of spermatozoa has become suppressed. He arrives 

 at this conclusion in the face of an overwhelming body of evidence 



