30 SUMMARY OF CURRENT RESEARCHES RELATING TO 



The two accessory chromosomes come to the equator of the spindle in 

 the secondary spermatocyte with the five bivalents. making in all seven. 

 Each accessory now divides, so that the resulting spermatids each receive 

 seven chromosomes — that is, five bivalent, plus two accessory, or the 

 equivalent of twelve univalent chromosomes. In reality, then, of the 

 total number of spermatids half have in all probability received ten and 

 half twelve (10 + 2) univalent chromosomes. Inasmuch as the sperma- 

 tids transform directly into spermatozoa, there must be two classes of the 

 latter, differing with respect to whether they have or have not the two 

 accessory chromosomes. It is a significant fact that approximately half 

 the resting spermatids, when strongly decolorized after iron-hrematoxylin 

 staining, show two chromatin nuclei and half do not. It seems probable 

 that these nucleoli may correspond to the accessory chromosomes, and 

 are to be identified with the two nucleoli of the primary spermatocyte 

 and the two eccentric chromosomes seen in the spermatogonia. It is 

 probable that in man and certain other Vertebrates, as also in the Insects, 

 Myriapods, and Arachnids, the accessory chromosomes are in some way 

 associated with the determination of sex. 



Mammalian Spermatozoon.* — J. van Molle has studied the sperma- 

 tozoon in squirrel, mole, guinea-pig, and rat. He finds that the sheath, 

 or " manchette," is of nuclear origin, and that it persists in the fully- 

 formed spermatozoon. The centriole is of an elbow-like (?) (equerre) 

 form, and retains this through the transformations of the tail and 

 middle-piece. The " baton-like body," the transverse branch of the 

 "centriole equerre," is not an ephemeral element, but persists till the 

 spermatozoon has its final form. 



Inheritance of Skin-pigmentation in Man.f — Gertrude C. Davenport 

 and Charles B. Davenport have made a careful study of the inheritance 

 of skin-pigment in typical Caucasians and in crosses between whites and 

 negroes. They have also made a study of the inheritance of albinism 

 in man. The conclusion from various data, qualitative as well as 

 quantitative, is that skin-colour in negro and white crosses is not a 

 typical " blend," but that, on the contrary, the original grades of heavy 

 and slight melanogenesis segregate in the germ-cells — often imperfectly, 

 because of the multiplicity of units (or grades) for skin-pigmentation— 

 and thus the original colour characters are more or less perfectly restored. 

 All studies indicate that blondes lack one or more units that brunettes 

 possess ; that the negro skin possesses still additional units : that 

 individuals with the heavier skin-pigmentation may have slight pig- 

 mentation covered over (hypostatic), evidence of this condition appearing 

 in the light offspring of such hybrids in the second or third generation ; 

 and that first-generation hybrids frequently show, somatically, a colour 

 grade less than that which they carry potentially and may segregate in 

 their germ -cells. 



Sterility .| — Max Morse has brought together a number of facts 

 bearing upon the difficult problem of sterility. " As far as may be 



* La Cellule, xxvi. (1910) pp. 425-49 (1 pi.). 



t Amer. Nat., xliv. (1910) pp. 641-72. J Tom. cit., pp. 624-33. 



