270 NATURAL HISTORY SOCIETY OP DUBLIN. 



nation of the phenomenon of conjugation from Cylindrocystis andMeso- 

 tsenium into other genera of the Family, and briefly to trace some of 

 the modifications displayed, and to consider how far they bear upon the 

 question. In these we find a certain greater or less amount of complex- 

 ity in the conditions contemporaneous with, and subsequent to, the act, 

 which are so constant in their recurrence as I think strongly to evidence, 

 when we consider it, that the phenomenon is by no means casual or 

 insignificant. 



In the first place, in our genus Mesotaenium, the process of conjuga- 

 tion takes place by a protrusion and simple fusion of the primordial utri- 

 cles and contents of each pair of cells, the parent cell- wall slipping off 

 in the act, and becoming discarded, and finally dissolved. The conju- 

 gating cells lie in a great variety of positions, and the different zygo- 

 spores are of course at first of very varying outlines; but eventually they 

 assume externally a subquadrate or elliptic figure, and a proper cell- 

 wall. Again, in Cylindrocystis mutual lateral processes of the two con- 

 jugating cells are put forth, which inosculate, permitting the fusion of 

 the cell- contents of each. The isthmus between the two gradually 

 grows wider, until the zygospore, from a form somewhat like an H or an 

 X, by-and-by assumes a subquadrate outline ; eventually, the wall of 

 the parent cell giving way at their suture, and becoming by degrees 

 thrown off, the zygospores having acquired a proper cell- wall. In nei- 

 ther genus does the zygospore bear spines. In the germination of the 

 zygospore, in both genera, there are developed four daughter-cells, each 

 of which becomes the primordial individual of a new cycle, thus repro- 

 ducing the species. 



Now, these cases — those of the plants in question, which I have 

 thus so briefly alluded to — seem to present the simplest conditions in 

 which the phenomenon of conjugation occurs. Here the contents of two 

 cells., seemingly morphologically equivalent, and apparently of similar 

 value, become fused into one, outside either parent cell; and it is at least 

 noteworthy that the first result of the fusion of the two distinct pri- 

 mordial cells, as indeed in all cases of conjugation, is the formation 

 of a new cellulose wall round each zygospore produced by the act ; and 

 this is precisely what takes place when the oospore in Vaucheria, CEdo- 

 gonium, Sphoeroplea, &c, becomes fertilized by the spermatozoids. 

 Likewise, the circumstance of the zygospore of Cylindrocystis and Me- 

 sotaenium producing in germination four daughter-cells has its analogy 

 in the same behaviour in the germination of the oospore of CEdogonium 

 and Bulbochaete — which fact thus, so far as it goes, seems to point to the 

 conclusion that in each they are the result of a similar act. The 

 daughter-cells, or primary cells of the following generation, however, 

 in each differ in what I should but regard as a secondary and unessential 

 circumstance, in that, in CEdogonium and Bulbochsete, they are for a 

 time motile, whilst in the parallel degree of development of the spore of 

 Cylindrocystis and Mesotaenium they are, as always, still. 



Examples of conditions nearly as simple are presented by many Des- 



