90 HICK : KLEIN ON THE GENUS VOLVOX. 



protoplasts into physical connection with one another, or whether 

 they are interrupted midway by a ' middle lamella.' He pronounces 

 in favour of the latter view, without, however, contending that such 

 a condition obtains in all cases without exception. My own obser- 

 vations long ago led me to the conclusion that the threads were 

 continuous, and so far a re-examination of my preparations and of 

 fresh material has only confirmed me therein. But Klein appears 

 to hold strongly to his view of the state of affairs, and in the face of 

 this it would be unwise to insist upon a contrary view until a further 

 investigation has been made, and his methods of treatment have 

 been tested. 



It will be noticed that in the above diagnosis the monoecious 

 and dioecious conditions are not mentioned, whereas by Cohn they 

 were emphasised and utilised as important specific distinctions. 

 Klein, however, shows that they are not so constant as has been 

 supposed, and that parthenogonidia, antheridia, and oogonia may 

 occur in nearly all possible combinations, either simultaneously or 

 successively. 



Seasonal Duration of the Various Colonies. — Stein and 

 Cohn interpreted the life-cycle of Volvox as an alternation of 

 generations, the asexual colonies occurring first and for a long period, 

 and the sexual ones later on, or on the drying-up of the pond. 

 Klein finds, however, that the relations of the various colonies are 

 much more complicated than this interpretation would lead us to 

 expect. In Volvox aureus ase.xual propagation goes on abundantly 

 in the early spring, but soon dioecious sexual colonies make their 

 appearance, and the normal alternation is completed. But while 

 this occurs in a part of the asexual series, the rest continue to 

 multiply asexually into the summer, and form what Klein, for 

 brevity, names the summer series. When subsequently sexual repro- 

 duction occurs in this series, the distinction between sexual and 

 asexual colonies appears to be partially or entirely lost. The history 

 of this summer series, combined with that of the earlier one, leads 

 Klein to the conclusion that in Volvox aureus the alternation of 

 generations occurs in three ways : a normal typical one, in which the 

 asexual generations are followed by dicecious and pure sexual 

 colonies, and two others which he considers as phenomena of 

 adaptation. In one of the latter the series of asexual colonies is 

 followed by dioecious sexual ones, but the males are not pure, seeing 

 that, besides antheridia, they contain parthenogenetically produced 

 daughter colonies. In the third form of alternation the asexual 

 generations are followed by sexual viomxcious colonies which are 

 firoterogynous. Into the further complications which occasionally 



Naturalist, 



