Chrowatin as ''Hereditary Sfihsfance'' 347 



making out tliat there are two sorts of spermatozoa from 

 one and tlie same male in certain insects, the difference be- 

 tween the two being that the head of one kind contains an 

 element or body not present in tlie other. At first there was 

 difference of view as to the anatomical nature of this extra 

 element. Some regarded it as akin to the nucleolus rather 

 than to the chromosomes. The idea of dimorphic sperma- 

 tozoa was first clearly expressed by H. Henking as follows, 

 "I believe every unbiased observer will view with me this 

 spherical element [of the sperm head] sliarply distinguish- 

 able from the otlier chromatin, as the nuclear body [present 

 in part of the speraiatids]. Thus is revealed the important 

 fact thht we have two kinds of spermato::oa : one kind pos- 

 sesses a nucleolus, the other does not.'''' ^■' 



C. E. McClung, another student of spermatogenesis, first 

 suspected that these two kinds of spermatozoa have some- 

 thing to do with the two sexes. The important paper in 

 which this hypothesis is set forth was published in 1902, 

 and within the brief period since that date, the hypothesis 

 has been supported and extended by such a mass of obser- 

 vation that its universality for at least the animal kingdom 

 seems not improbable. 



The exact terms in which McClung stated the hypotheses 

 merit attention. He says, "Briefly stated, then, my con- 

 ception of the function exercised by the accessory chromo- 

 some is that it is the bearer of those qualities which pertain 

 to the male organism, primary among which is the facult}^ 

 of producing sex-cells that have the fqrm of spermatozoa." ^'' 

 Noteworthy for our discussion is the difference of view 

 concerning the chemico-morphological nature of the extra 

 element in the spermatozoan as shown by these two quota- 

 tions. It was regarded as sharply distinguished from the 

 chromosomes by Henking, but as a true chromosome by Mc- 

 Clung. The great preponderance of later opinion has sided 

 with McClung, but very recently the question has been 



