THE BIONOMICS OP CONVOLUTA EOSCOFFENSIS. 373 



Convoluta duriug its first fortnight's free existence, and is 

 figured on PI. 31, figs. 12 — 16. Within this mass digestion 

 occurs. Alga3 remain for a long time unaltered, but diatoms 

 are soon resolved into a brown granular fluid and empty 

 valves (PI. 31, figs. 10, 11). Other remains of food are seen 

 in the dumbbell-shaped masses seen in fig. 9. 



The wandering cells circulate as well as digest the food. 

 Diatoms in process of disintegration are met with in the 

 anterior part of the body and in the lateral parenchyma, as 

 well as in the central syncytium, or "gut" (PI. 31, fig. 9). 

 The close contact between such food-laden wandering cells 

 and the green cells suggests that the latter may in this way 

 receive their nitrogenous supplies. 



The course of the food may also be followed by the use of 

 litmus, indigo, methylene-blue, lamp-black, and other sub- 

 stances. Methylene-blue, for example (fig. 6), is taken up 

 by wandering cells, and after a time appears in a diifused 

 fluid form in the meshes of the syncytium. Litmus is carried 

 in great quantities to the peripheral parenchyma. Congo red 

 is equally well distributed by the agency of the active cells 

 (PL 30, fig. 5). Sodium sulphindigotate is treated in the 

 same manner, and though it is often used as a natural injection 

 to demonstrate excretory tissues, we have seen no trace of 

 an excretory system. After several months of daily examina- 

 tion of Convoluta at all stages of development, and after 

 the employment of substances that are specifically excreted 

 in other animals, we have not seen a flame-cell or a canaliculus. 

 We have, however, repeatedly seen the "pulsellas" observed 

 by Geddes (1879) and Delage (1886), both in larval and 

 adult forms, but we are unable to suggest what their nature 

 or function may be (PI. 31, figs. 17, 18). 



Whereas the outer surface of Convoluta is strongly 

 alkaline, the central syncytium, or " gut," is strongly acid. 

 The former reaction is probably due to the secretion of the 

 skin-glands, which, according to Geddes, contain a volatile 

 base, probably trimethylamin, the source of the potent smell 

 and poisonous action of Convoluta. The latter reaction can 



