1890.] [Ryder. 



examples, no less than in the fact that the polarity of young, viviparously 

 developed aphides corresponds to the fore and aft polarities of the parents. 

 Or, as in the case of the ovarian leaflets of the ovary of the lamprey, the 

 micropyles are found to be invariably turned towards the vascular core 

 of the leaflets, and consequently towards the sources of nutriment and 

 oxygen. In this last case also, these factors have determined the position 

 of the future germinal or animal pole, and consequently the point on the 

 egg where development shall begin. 



The points which have thus far been elaborated tend, in a general way, 

 to support the conclusion that, in the production of ova and spermatozoa, 

 both have arisen from a common basis. The lowest forms, we certainly 

 know, tend to multiply without attendant karyokinetic processes, prob- 

 ably, as suggested, because a cytoplasmic field or arena in which nuclear 

 movement is possible, is wanting. In the lowest Monads sporulation re- 

 sults in the breaking up of the parent body into infmitesimally minute 

 germs, which are, presumably, composed in the main of chromatin or 

 nucleoplasm, a conclusion which comports with the fact now ascertained, 

 that the chromatin or nucleoplasm of lower forms, if deprived of its 

 envelope of cytoplasm, may regenerate it. Overgrowth of mass, so as to 

 form a large cell-body composed of cytoplasm, is unknown amongst the 

 very lowest forms, which are also flagellate. In the next step (Nostoc), 

 the overgrowth of certain cells means that they are incapable of develop- 

 ment. In the next step, the conjugation of overgrown cells, with those 

 in which nucleoplasm preponderates, restores the power of growth or the 

 power to integrate cytoplasm anew, or, as in Infusoria, conjugation stim- 

 ulates the production of nucleoplasm through the constructive metabolism 

 of the investing cytoplasm. 



All of this evidence tends to prove that maleness, or the condition of 

 the flagellate spore, is the primitive one as already stated. Since the very 

 lowest animal forms are likely to preserve some reminiscence of the primi- 

 tive processes leading up to animal sexuality in its most generalized form, 

 it will be desirable to appeal to the evidence offered by such forms. The 

 Amoeba is undoubtedly animal in nature, but notwithstanding the persist- 

 ence and frequency with which it has been studied, much still remains to 

 be learned of its life history. 



Leidy has shown that, in certain forms of Amoeba, the nuclei tend to 

 multiply after reaching a certain size, and through a tripartite division 

 without karyokinesis. One of these nuclei is then transported to near 

 the surface, where it bursts and allows the balls of chromatin adherent to 

 its walls to escape into the surrounding water, presumably as germs, but 

 he did not trace their history. If this should prove to be a true case of 

 sporulation, it would prove that in the Amoeba there are conditions which 

 favor the production of chromatin, and that the germinal matter or nucleo- 

 plasm is "set aside " in the nucleus from which it is expelled. 



Mrs. Lillie Holman's observations (I. c. supra) also tend to show that a 

 conjugation may occur where one Amoeba swallows another and then 



