94 



Edmund B. Wilson 



Despite the apparent diversity of the types that have been enu- 

 merated all conform to the common principle that the spermatozoa 

 are of two classes, equal in number, that are respectively male 

 producing and female producing. In the case of Type I this is no 

 more than an inference, since the two classes cannot be distin- 

 guished by the eye; but its great probability will be admitted in 

 the fact that the forms with equal idiochromosomes are connected 

 by forms (such as Mineus) in which only a slight inequality exists, 

 with those in which the inequality is very marked (Wilson 

 '05a). The facts now show that the difference between the two 

 classes of spermatozoa is not always confined to a single pair 

 of chromosomes, but may affect two pairs (Syromastes) or even 

 a larger number (Galgulus). It is noteworthy that in every case 

 where a quantitative difference of chromatin exists between the 

 sexes it is always in favor of the female, whether it appear in a 

 larger number of chromosomes or in the greater size of one of them. 

 But I must again emphasize the fact that this quantitative differ- 

 ence cannot be considered as the primary factor that differenti- 

 ates the two classes, for in the first class such a difference does not 

 exist,^^ while in Metapodius, even in the same species, it is some- 



'^ I based this type on the facts observed in Nezara, where the idiochromosomes are equal in size in 

 both sexes. This is not in accordance with the later observations of Montgomery ('06) who believes 

 that in the Hemiptera generally the two components (paternal and maternal) of every chromosome 

 pair are at least slightly unequal — though he finds the idiochromosomes of Oncopeltus equal as I have 

 also since observed. A reexamination of Nezara confirms my original account of this form, though in 

 some individuals the idiochromosomes often appear very slightly unequal. A careful examination 

 of the other chromosomes, particularly the small ra-chromosomes (which are most favorable for the 

 purpose) in Alydus, Anasa, Archimerus, Pachylis, and other genera, leads me to a very skeptical view of 

 Montgomery's general conclusion on this point. It is true that the two members of each pair vary 

 slightly in relative size, and are not always exactly equal; but, in my material at least, it is clear that 



