190 TRA^•SACTIO^'S and proceedings of the [Sess. lxiii. 



occurred ; the ultimate member of the series, where com- 

 plete conjugation has occurred, is figured in Fig. 14. 



Fig. 15 shows a case of a dumb-bell shaped zygospore 

 with three cells similar to that in Fig. 7 for two cells. 

 West figures a further case for three cells, where, owing 

 to the lateral pressure of one of the male tubes, con- 

 jugation by way of the other is prevented, and azygospores 

 result. 



Figs. 16 to 20 illustrate the case of attempted conjuga- 

 tion between three cells, two of which are female and one 

 male. In Fig. 16, the male cell sends out two tubes to 

 meet those of the two females, but conjugates with one of 

 them. Fig. 18 is a transition to the following. In 

 Figs. 17 and 19, the single male cell sends out a broad 

 tube which bifurcates, each branch meeting a tube from 

 each female cell. In Fig. 20 is seen the condition where 

 the single broad male tube is faceted to meet the two 

 females produced in very close proximity (as if for lateral 

 conjugation). 



The ultimate stage of this series, where one male would 

 fertilise two females, either by way of one or by two 

 separate tubes, was very carefully looked for. This would 

 involve the division of the male protoplast immediately 

 prior to the act of conjugation. That this might occur 

 might be reasonably expected from what has been already 

 described as occurring in Fig. 7, which is the converse 

 where only part of the contents of a female cell have con- 

 iugated with the male gamete, the other part of the female 

 protoplast remaining sterile. Given that this sterile part 

 conjugated with a male cell, then there would be two 

 zygotes in the female cell as the result of conjugation of 

 three, and the opposite case for the single female cell 

 would be realised. Examples were looked for where 

 active nuclear division occurs at the apical cells of the 

 filaments, and, although such exhibited irregularities of 

 conjugation depicted in Figs. 21,22, and 23, the particular 

 case was not met with. 



A study of artificial cultures leads one to note particu- 

 larly the nice adaptation to environment displayed by the 

 alg£e.^ The internal forces of the colls ajipear to be so 

 accurately balanced by the external conditions that a sort 



