ASTASIADJE. 



105 



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

 cellular algje and fungi ; still the analogy to the developmental 

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

 Spumella vulyaris (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 Chromulina 

 nebulosa Cnk., and Ochracea Ehrbg. 



A second group nearly allied to the Algaj (Protococcace(i) 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. 



FIG. 131. Eujtena viridis. a and J.free swimming, in different states or contraction. c t d,c, 



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 ylobator, Gonium pectorale, Ste- 

 phanosphasra pluvialis. 



The Astasiadce are contractile unicellular Flagellata, which are 

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



