REPRODUCTION AND SEX 191 



exception to the statement that has just been made as to 

 the difference in constitution between conjugating and non- 

 conjugating reproductive bodies. It shows that a gamete 

 is a complete, if undeveloped, individual (pp. 183, 528). 

 With the reproductive processes of Hydra it is not 



difficult to compare those of the Ciliata. These 

 Re production animals, though they are not divided into cells, 

 protozoa. possess, as we have seen, a body nucleus or 



meganucleus, and a germ nucleus or micro- 

 nucleus. The ordinary fission is asexual reproduction, 

 each nucleus contributing to both offspring. The so-called 

 " conjugation " of the Ciliata is an act of sexual reproduction, 

 consisting in the formation of germs, their union, and a de- 

 velopment of the zygote (p. 135). The difference between 

 the germ formation of the Ciliata and that of the Metazoa 

 is due to the absence of body-cells in the former. 

 The body nucleus is destroyed within the parent body 

 so that the latter becomes a germ as well as the 

 portion which separates from it. Thus there arise two 

 germs, of which one has little if any cytoplasm and is a 

 male gamete, while the other, which keeps most if not all 

 of the cytoplasm of the parent, is a female gamete. After 

 true conjugation, a process comparable to development 

 takes place. In the Sporozoa, also, both sexual and asexual 

 reproduction are found. The trophozoites give rise to a 

 number of germs which conjugate to form the sporonts. 

 The latter give rise asexually to the sporozoites, and from 

 these, when they have grown into trophozoites, there 

 presently appear sexual individuals again. There is not 

 in the germ formation of Sporozoa any such obvious 

 freeing of germ- from body-substance as is found in 

 Metazoa and Ciliata, but it may be that in the dis- 

 carding of the residual protoplasm some such separation 

 occurs. In Polytoma and Amoeba all the fissions are acts 

 of asexual reproduction. It may well be that the bodies of 

 these animals contain matter which is comparable to the 

 body-substance of the Metazoa, but there is in any case 

 no visible distinction between body- and germ-substance, and 

 in each act of fission the protoplasm is evenly divided. In 

 Polytoma conjugation occurs between ordinary individuals, 

 and is not part of an act of reproduction. In Amoeba 



