FATE OF NUCLEUS AND NUCLEOLUS IN COPULATION. 235 



There can be no doubt that both " nucleus " and " nucleolus " 

 have the function of a cell-nucleus. The Infusorian is, in other words, 

 provided with two quite different nuclei (a " principal nucleus " and an 

 " accessory nucleus "), both of which undergo at certain times (during 

 conjugation) a fundamental transformation and renewal. 



That the " nucleus " is really of the nature of a true cell-nucleus 

 is proved by the fact that under certain circumstances it also exhibits 

 the same changes as we have previously described in the case of the 

 " nucleolus." We know especially of some Infusoria in which con- 

 jugation has not yet been observed (Spirochona, Podophrya, Dendro- 

 cometes). Here it is not the "nucleolus" but the "nucleus" which 

 assumes a fibrillated character before division, and afterwards (in its 

 parts) reassumes its former state. Similarly, the later divisions in 

 Infusoria take place without change in the " nucleolus." It is only 

 the " nucleus " which participates in these processes, and falls (whether 

 with antecedent striation or not is still uncertain) into two equal parts, 

 one for each of the twin parts. 



The above observations sufficiently prove that conjugation is 

 of some consequence in the reproductive processes of the Infusoria. 

 It is, however, no sexual copulation; it can hardly be said to be 

 anything but a fertilisation, 1 as we have already hinted. At 

 any rate, the act is no concurrence of sexual products, but of living 

 individuals of individuals, however, which, like the sexual products, 

 are morphologically equivalent to cells, and as such represent in one 

 the various organs, tissues, and also sperms and ova of the higher 

 animals. We are confirmed in this opinion by the fact that 

 there are Infusoria (Vorticellce) in which conjugation never or seldom 

 occurs between individuals of equal size and similar form, but 

 between a large fixed animal and a much smaller young form, 

 which originates in consequence of a rapidly repeated division, and 

 stands in exactly the same relation to the fixed form that the micro- 

 gonidium bears to the macrogonidium in certain Algse a relation 

 which, in the case of the latter, had for long been jv.stly regarded by 

 botanists as equivalent to fertilisation. 



Conjugation is further of great importance in connection with the 

 Infusoria since the subsequent divisions occur much more frequently 

 than would otherwise be the case. It therefore obviously serves, like 

 genuine fertilisation, for " freshening the blood." It marks, to some 

 extent, the beginning of a reproductive period, during which multi- 



1 This being the case, we may note the great interest attached to the resemblance 

 between the fate of the nucleus in conjugating individuals and the changes of the germinal 

 vesicle which accompany impregnation, especially as described in the recent researches of 

 Hertwig, Fol, Biitschli, and others.. [See Geddes, article "Reproduction," " Encycl. 

 Brit.," Edinburgh, 1885. W. E. H.] 



