SCIENCE. 



[N. S. Vol. XI. No. 284. 



duced by different individuals. In the case of 

 hermaphrodites, the term applied to organ- 

 isms which produce both male and female 

 gametes in the same individual, there is 

 generally some arrangement which tends to 

 prevent the male gamete from conjugating 

 with the female gamete of the same parent ; 

 but this phenomenon is not absolutely ex- 

 cluded, and takes place as a normal phenom- 

 enon in many plants and possibly in some 

 animals. 



This fusion of the protoplasm of the two 

 gametes gives us a uninucleated organism 

 — for the fusion of the nuclei of the two 

 gametes seems to be an essential part of the 

 process — in which the potencies of the two 

 gametes are blended. The zygote, as the 

 mass formed of the fused gametes is called, 

 is formed by the combination of two indi- 

 vidualities, and is therefore essentially a 

 new individualitj^, the characters of which 

 will be different from the characters of 

 both of the parents. This fact, which is not 

 apparent in the zygote when first estab- 

 lished, because the parts are hardly distin- 

 guishable by our senses, becomes obvious as 

 soon as organs, with the appearance of 

 which we are familiar, are formed. As a 

 general rule this cannot be said to have oc- 

 curred until what we call maturity has been 

 nearly reached, because we are not familiar 

 enough with the features of immature or- 

 ganisms to detect individual differences. 

 But you may rest assured that such differ- 

 ences exist at all stages of growth from that 

 of the uninucleated zygote till death. How 

 the characters of the two parents will com- 

 bine in the zygote it is impossible to pre- 

 dict, and the result is never the same even 

 though the conjugations have been between 

 gametes of identical origin. There maybe 

 an almost perfect mixture, the blending ex- 

 tending to even quite minute details ; or 

 the characters of the one parent may pre- 

 dominate — be prepotent, as we call it — 

 over those of the other ; or they may blend 



in such a way that the zygote offers char- 

 acters found in neither parent. Or, finally, 

 the features of one parent may come out at 

 one stage of growth, those of the other at 

 another stage. But, however the char- 

 acters may blend, the product never exactly 

 resembles the parents. The extent to which 

 it differs from them is the measure of the 

 variation. 



To resume, it will be observed that in 

 the method of reproduction sometimes 

 called sexual, two distinct processes occur. 

 One of these is the real reproductive act, 

 which consists in the production by fission 

 of uninuclear individuals called gametes ; 

 the second is the fusion of the gametes to 

 form the zygote. The gametes are of two 

 kinds, and the reason of there being two 

 kinds is intelligible when we consider the 

 parts they have to play. The male gamete 

 is nearly always endowed with locomotive 

 power, and the female gamete is stored 

 with food material to be used by the zygote 

 in the first stages of growth. The destiny 

 of these two uninucleated organisms is to 

 fuse with one another, and so to give rise 

 to a zygote which ultimately assumes the 

 typical form of the species. As a general 

 rule the gametes have but a limited dura- 

 tion* of life unless they conjugate, and this 

 is quite intelligible when we remember that 

 they have no organs, e. g., digestive organs, 

 suitable for the maintenance of life. It is 

 rarely found that they have the power of 

 assuming the form of their parent, unless 

 they conjugate. This never happens in the 

 case of the male gamete (at any rate in 

 animals), and only rarelj'^ in that of the 

 female. When it occurs — that is to say, 

 when the ovum develops without conju- 

 gation — we call the phenomenon partheno- 

 genesis. Parthenogenesis is found more 



*Under favorable conditions they may live a con- 

 siderable time — e. g. , the spermatozoon of certain ants, 

 •which are stated by Sir John Lubbock to live in some 

 cases for seven years. 



