HEREDITY 191 



the formation of all the secondary sexual characters, is also refuted by 

 the following observations. There are cases of hermaphroditism known 

 in which the one side of the body contained a testicle, the other an 

 ovary. In hermaphroditic insects of this kind, it has been observed 

 that the secondary sexual characters differed also on the two sides, the 

 side with the ovary having a female, the other side a male antenna. 

 This would be impossible if a substance produced by the sexual glands, 

 and circulating in the blood, were the cause of the secondary sexual 

 characters. If, however, the primary as well as certain secondaiy 

 characters are already preformed in the egg, it might be well possible 

 that an egg was already female on one side and male on the other side. 

 Crampton grafted the heads of one sex upon the bodies of the other 

 sex in pupae of butterflies, in trying to find out whether the sexual 

 glands could influence the secondary sexual characters on the head, 

 but this was not the case. There are then certain secondary sexual 

 characters which seem to be determined before the sexual glands reach 

 the mature stage. Certain secondary sexual characters, of course, such 

 as develop at the period of sexual maturity, are determined by the 

 development of the sexual glands and fail to appear when these glands 

 are removed before the time of sexual maturity. 



3. Egg Structure and Heredity 



The form of the body as well as the instincts of the animal are trans- 

 mitted through the sexual cells. We are forced to assume that the egg 

 or the spermatozoon must possess a structure of a degree of complexity 

 equal to that of the adult, or that the development occurs in a manner 

 which renders such an assumption unnecessary. It is hardly necessary 

 to mention that we must choose the latter alternative. 



If we examine the living egg of a sea urchin or a starfish, we find 

 that its contents are chiefly Hquid. If such eggs are exposed to a shght 

 one-sided pressure, e.g. under the cover glass, the surface film or mem- 

 brane bursts, and the hquid contents can be seen streaming slowly into 

 the surrounding sea water. In this hquid minute granules are notice- 

 able, which may be sohd, but the main mass of the egg is hquid. The 

 nucleus is surrounded by a soUd film. It is possible or probable fhat 

 the chromosomes are, in a certain phase of cell division, sohd, or 

 possess a high degree of viscosity. This follows from the fact that 

 the form of each individual chromosome remains constant through 

 all cell divisions. It is obvious that a mass which is to a large extent 

 hquid cannot possess a structure of such a degree of complexity as 

 the adult starfish or sea urchin. Moreover, we can observe 'directly 



