rSVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 405 



the end of the period of heat of the female, a male may be expected 

 to be generated. On the other hand, a morbid condition or malfor- 

 mation of the female generative organs, or a scantiness of sperm in 

 the male, should result in the production of a female. Among 

 actual facts which bear out these theoretical considerations are cited 

 twenty experiments made by Dr. Heitzmann ; of these, twelve bore 

 out the prediction previously made as to the sex to be expected. 

 It is a known fact, confirmed by experiments made with poultry, 

 that an old male generates more males than females, and vice versa 

 with a yoiing one. This may be explained, in accordance with the 

 hypothesis, either on the assumption that the semen is more con- 

 centrated as a rule in an old male, or that copulations being less 

 frequent in such cases, the spermatozoa would be more abundant. 



The ovum may develop without contact of semen, i. e. parthcno- 

 genetically, in which case the sex of the offspring will be always the 

 same for the same species, or if receiving a minimum amount, will 

 go through merely the primary stages of development, and will abort ; 

 or it may receive a greater amount and produce a female, or a still 

 greater amount and a male will be the result. 



Origin of the Sexes.* — Dr. Nussbaum concludes a paper of 

 120 pages by pointing out that the differentiation of the sexes is not 

 due to the association of the two previously united functions with two 

 different series of descendants of a common rudiment, but that it is 

 rather due to the variation of homologous cells, with a view to the 

 more complete success of conjugation. The ova and spermatozoa are 

 derived from equivalent cells, and the first differentiation of the sex 

 lies in the greater amount of division undergone by the male genera- 

 tive cells ; this is seen in plants as well as in animals. Then, the 

 ovarian cell remains passive, while the male exhibits amoeboid or 

 ciliated movements. As we ascend in the scale of organization, other 

 differences become added on to the difierence in character of the 

 tissues of the glands and of the efferent ducts, which themselves only 

 appear at a comparatively late period. Differences in the appendages, 

 in external form, in instinct and intellect, thus appear, and the " male " 

 and the " female " are completely distinguished. 



Dichogamous Animals, t — M. Canestrini calls attention to the 

 fact that the phenomenon of dichogamy, so often occurring in the 

 vegetable kingdom, takes place in the animal kingdom also, citing 

 the Cestodc worms as a case in point. The male sexual organs of 

 a segment are first matured, and later the female organs; a proglottis 

 is therefore unable to fertilize itself, but can be fertilized by the next 

 following proglottis of the scries. Animals such as these may bo 

 called dichogamous and protcrmulroiis. In some Gastcropodous Mol- 

 luscs, whicli arc hermaphrodite, the sexual elements might meet within 

 the hermaphrodite gland, but as a fact copulation is the rule, because 

 the elements are not mature at tlio same time. Similar facts have 

 been observed in the oysters and other Lamellibrauchs. 



* 'Arch. Mikr. Anat.,' xviii. (1880) p. I. 



t • Bull. Soc. Von.-Trent. Sci. Nat.,' i. (1879) p. '22. 



