ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 461 



In castrates the supra-renals show an increase, in spayed rats a 

 decrease. When the spermatic cords are ligatured (and the testis 

 absorbed) the supra-renals show reactions similar to those following 

 castration. The thymus increases to about twice its size after gonadectomy. 

 It seems not only to delay its normal involutionary process but actually 

 to increase in weight. The weight of the hypophysis is increased on 

 the average by 50 p.c. after removal of the testis or after ligature of the 

 spermatic cord (and absorption of the testis). On the other hand, 

 spaying produced only a slight increase (about 8 p.c. on the average). 



After removal of the sex glands and compensatory growth of the 

 hypophysis, there is no overgrowth of the body or obesity. But these 

 responses appear when the enlargement of the hypophysis does not 

 occur — in the spayed rats, for example. In the semi-spayed and semi- 

 castrated, neither enlargement of the hypophysis nor obesity occurs, for 

 the enlargement of the remaining gonad enables it to furnish the 

 normal amount of gonadine. The total removal of the gonads tends to 

 increase the resemblance between the two sexes, or it may be said that 

 gonadectomy favours the production of the secondary sex-characters 

 of the opposite sex. 



Hybridization among Ducks and Pheasants.* — John C. Philipps 

 has made a number of interesting crosses, e.g. pintail and mallard, Anas 

 tristis and mallard, Black East India duck and mallard, Lady Amherst 

 Pheasant and Golden Pheasant. Many characters apparently clear-cut 

 and antagonistic do not segregate clearly. It is almost certain that the 

 ordinary sub-species of the ornithologist is very far from being a unit 

 variation. In the wild forms experimented with, both sexes carry the 

 characters of the opposite sex through several generations without an 

 additional " dose " of the character in question, but it is admitted that 

 sex-linked inheritance may be a feature in domestic races. A study of 

 species hybrids in birds will satisfy anyone that on almost every feather 

 region the minutest details of feather pattern and colour show the 

 influence of both parental races. Only in sterile hybrids, or hybrids 

 between distantly related forms, do we find hybrids that are at all 

 puzzling in appearance, as Ghigi has pointed out. In crossing two 

 species, only one of which is sex dimorphic, a more primitive type of 

 male plumage is seen in the hybrids and in the back crosses. In the 

 mallard, a condition closely resembling eclipse or summer plumage is 

 brought out by crosses with the black duck. 



Inheritance in Teleost Hybrids.f — H. H. Newman has made 

 reciprocal crosses between species of the genera Fundulus and Cyprinodon, 

 and between species of the genus Fundulus, four of the hybridizations 

 resulting in more or less viable larvae. The most successful crosses are 

 those between F. diaphanus aud F. heteroclitiis, in spite of the fact that 

 the former is a fresh-water species and the latter a marine species. It 

 seems generally true that in crosses between very closely related species 



* Journ. Exper. Zool., xviii. (1915) pp. 69-112 9 pis.). 

 t Journ. Exper. Zool., xvi. (1914) pp. 447- 90 (5 pis.). 



Oct. 20th, 1915 2 k 



