THE INFUSORIA 395 



During the whole of the somatic life, that is to say, between the acts 

 of fission and conjugation, the micronuclei remain extremely small, 

 the chromatin being concentrated into an extremely minute granule, 

 and there can be little doubt that they are in a condition of 

 rest. 



During conjugation, however, the relative activity of the two. 

 nuclei is reversed. The micronuclei enlarge, divide by mitosis, and 

 show other signs of extreme activity. It is the products of the 

 division of micronuclei alone that fuse to form the cleavage nuclei. 

 The meganuclei, on the other hand, degenerate and disappear. 

 The evidence, therefore, is conclusive that the meganucleus is a 

 somatic nucleus, and may be compared with the nuclei of the cells 

 of the body of a Metazoon, and that the micronucleus is a sexual 

 nucleus, and can be only compared with the nuclei of the sexual 

 cells of the Metazoon. 



There is very little evidence, however, that there is allocated 

 to each micronucleus in the Infusorian's body a specialised part of 

 the cytoplasm, as there is in the Metazoon. There is, in other 

 words, evidence of a sexual nucleus, but very little evidence of 

 sexual cytoplasm. If we assume that such sexual cytoplasm does 

 exist, and that during the act of conjugation the sexual cytoplasm 

 of the two individuals mingles, the parallelism between the sexual 

 act of the Infusoria and that of the Metazoa is established. 



But without making any assumption whatever, it is clearly 

 erroneous to compare the conjugation of two Infusorians with the 

 conjugation of an ovum and a spermatozoon. The degeneration of 

 the meganucleus after or during conjugation clearly proves that 

 the Inf usorian is something more than a mere sexual cell or gamete. 

 It is only a part, and a very small part too, of the whole body of 

 the Infusorian that functionally conjugates, the remainder is only 

 accessory to the act. It is therefore only misleading to call the 

 stalked Vorticella a megagamete and the free-swimming individual 

 that becomes attached to it a microgamete. These individuals 

 have all the essential features of female and male individuals, and 

 the act that they perform is essentially an act comparable to the 

 copulation of the Metazoa. Similarly, the conjugating individuals of 

 the Holotricha ought not to be called Isogametes, but hermaphrodite 

 individuals. 



An important and interesting question then arises as to the 

 individuality of the Infusoria before and after conjugation. The 

 destruction of the old somatic nucleus during conjugation is proved, 

 but there is also evidence of a less satisfactory nature that the 

 somatic cytoplasm undergoes regeneration after the act. If it be 

 assumed that the old somatic cytoplasm is gradually replaced by 

 the conjoint sexual cytoplasm of the two conjugates, then the 

 individuality of the Infusorian before and after conjugation is not 



