VOLVOCINID^ ASTASIAD,*;. 



195 



In their whole developmental cycle they agree very closely with uni. 

 cellular algte and fungi ; still the analogy to the developmental 

 processes of many Infusoria, Atnpliileptus, is not to be passed over. 

 Spwmella vulgaris (termo Ehrbg.) of Cienkowski shows a somewhat 

 different development and cyst formation ; it receives solid food (by 

 aid of the food vacuoles) and is fixed by a fibre, as also Ckromulina 

 nebulosa Cnk., and Ochracea Ehrbg. 



A second group nearly allied to the Algre (Protococcacea) is that of 

 the Volvocinidce. These organisms consist of colonies of cells united 

 by a common gelatinous substance, and the following characteristics 

 indicate their close relationship to the Algse : (1) in the inactive 

 stage they possess a cellulose membrane ; (2) they exhale oxygen ; 

 (3) they possess an abundance of chlorophyll and of vegetable red or 

 brown coloured oils. 



PIG. 134. Ettfflena viritHs. <? and 6,free swimming, in different states of contraction, c, d, e, 



encysted and in process of division. 



During the motile stage they possess the power of reproduction, 

 since the individual cells give rise to daughter colonies inside the 

 mother colony. A sexual reproduction (conjugation) has also been 

 shown. Certain of the mother cells increase in size and divide into 

 numerous microgonidia corresponding to spermatozoa ; others grow 

 to large ovicells, which are impregnated by the former, and then 

 surround themselves with a capsule, and sink to the ground as large 

 star-shaped cells. They also reproduce themselves during their 

 period of inactivity by fission within the cellulose capsule, while at 

 the same time a change of colour takes place. Amongst the best 

 known of the Volvocina are Volvox globator, Gonium pectorale, Ste- 

 phcmosphcera pluvialis. 



The Astasiadce, are contractile unicellular Flayellata, which are 

 allied to the Volvocinidce in their life phenomena, but they take up 



