190-">.] The Bionomics o/ Convolute Roscoffensis, ct<-. 95 



v. Contrary to Georgevitch's statement, when hatched from egg- 

 capsules placed in sterilised water, Courolutas are found, in a 

 certain number of cases, to develop green cells. Hence either 

 the green cells are not the result of infection, or infection may 

 take place from the capsular flora. 



j. The latter alternative is probably correct, for the more precautions 

 are taken to protect hatching Convoluta from infection, the fewer 

 are the cases in which green cells or their colourless antecedents 

 make their appearance in the animals. 



<j. The colourless antecedents of the green cells are first seen in the 

 gut, just above the mouth. 



D. Conditions. Direct proof of infection is lacking. The evidence, 

 however, points most strongly to infection. The infecting organism is 

 a colourless cell. Infection often takes place from the capsule. The 

 situation and colourlessness of the infecting cell suggest the view that 

 this cell is a saprophytic stage in the life history of the green cell. 

 Such saprophytic colourless stages are well known in green algae, 

 diatoms, and flagellates (Kriiger, 8 Karsten," Dangeard 10 ). 



The colourless cells are taken up in company with other organisms. 

 A pure culture is made from this mixed infection in the gut of the 

 animal. There the cells divide and, contained in wandering cells, are 

 carried to their final station in the periphery of the body. Some 

 remain colourless. The majority become green. 



We regard the presence of the green cells as due to a peculiar and 

 special case of phagocytosis, in which neither green cell nor wandering 

 cell is destroyed. 



The facts do not lend support to the view that the relation between 

 animal and alga is symbiotic. 



The green cells undoubtedly derive food from the animal. The 

 animal derives but little if any food from the green cells. We regard 

 the green cells as facultative parasites. In their relationship to their 

 host they recall, in some measure, such cases as Odorochytrium lentnce and 

 other green algae which live in the leaves of aquatic and other plants. 



III. Trojjisms. 



A. Previous Observations. Geddes (1879) first recorded positive 

 phototropism (phototactism). Von Graff' and Haberlandt (1891) 

 observed negative geotropism in stillness, positive geotropism in the 

 presence of vibrations. 



B. Observations of tJie Authors. a. Geotropism. The observations 

 cited above were confirmed. The young at hatching react to gravity 

 in the same way as adults. In the absence of the otolith, geotropism 

 does not occur. 



The reflex mechanism involves the anterior end of the body. The 

 hinder end of animals divided transversely does not react to gravity. 



