ZOOLOGY AND BOTANY, MIOROSCOPY, ETC. 559 



Both this species and V. globator vary remarkably in the size and 

 number of the cells of which the colony is composed, in the size of the 

 colony, and in the number of daughter-colonies, oospheres, oosperms, and 

 bundles of antherozoids ; while the size and form of the oosperms are 

 nearly constant in both species. The two species are best distinguished 

 by the form of the separate cells, and by the fact that the cells of 

 V. aureus are always at a considerably greater distance from one another 

 than those of V. globator. The separate cells of V. aureus are roundish 

 when seen from the surface, and are connected with one another by 

 extremely fine threads of protoplasm which are interrupted in the 

 middle ; while the much smaller cells of V. globator are angular in 

 outline, and are connected by much stouter threads of protoplasm 

 which are also interrupted. The colonies of V. aureus have very com- 

 monly an ellipsoidal or lemon-form. The protoplasts are invested 

 by a thick gelatinous membrane which does not show the reactions 

 of cellulose ; the interior of the coenobe is not filled with water, but 

 with jelly. 



When the daughter-families are being formed, the mother-colony 

 remains passive. The movement of the colony is the result of rotation 

 round an axis oblique to the path of motion. The young oospheres are 

 connected with the adjacent vegetative cells by a number of connecting- 

 threads. The bundles of antherozoids are formed from their mother- 

 cells by radial division, just as the daughter-families are formed from 

 the parthenogonids and germinating oosperms; the number of these 

 bundles may amount, in the purely male colonies, which are known 

 as Spheerosira Volvox, to over 1000 ; the antherozoids always escape 

 in bundles, which are formed in succession, and only separate later and 

 gradually. 



Volvox aureus is neither purely non-sexual and dioecious, nor purely 

 non-sexual and monoecious-proterogynous, but displays almost all possible 

 combinations in the distribution of the sexes ; Dr. Klein enumerates as 

 many as ten of these combinations. The coenobe must be regarded, from 

 a physiological point of view, as an example of commensalism for the 

 purpose of nutrition, and the author compares it to a bee-hive, where a 

 small number of individuals, which are exclusively concerned with the 

 reproduction of the species, live on the labour of the rest ; the partheno- 

 gonids, the oospheres, and the bundles of antherozoids, are nourished by 

 the vegetative cells. The reproductive organs always lie in the part of 

 the colony which is posterior when in movement. 



The alternation in the appearance of the sexual organs coincides with 

 the changes of the seasons. In the spring there are found chiefly non- 

 sexual or purely dioecious colonies, in the summer antherozoids only in 

 otherwise vegetative colonies, in the late summer and autumn also the 

 moncecious-proterogynous families, and vegetative colonies. The alterna- 

 tion of generations may close either, as is usually the case, with dioecious 

 purely sexual, or with monoecious-proterogynous colonies. 



From considerations derived from the history of development, 

 Dr. Klein regards the bundle of antherozoids of Volvox not as an 

 antherid, but as a male colony, and as homologous with an entire 

 coenobe ; each antherozoid invested in its envelope of mucilage is an 

 antherid, and homologous with an oogone and its single oosphere. It is 

 possible to have three generations, one inclosed within another, and all 

 fully developed. 



2 Q 2 



