316 Transactions of the Society, 



had taken three days. Its shell, also, though still thin compared 

 with a normal one, was stronger and thicker than in the two other 

 cases, where from beginning to end it had remained a thin pellicle. 

 And if I take into consideration two more individuals, born as 

 swimming larv?e from an act of division, but perfectly similar to 

 those produced by transformation, and which developed up to the 

 construction of a very thin and inadequate shell, I think we can 

 infer as a general rule that specimens isolated under the cover are 

 not to be expected to build a perfect envelope. In my opinion 

 this is because their swimming state lasts too long ; they look in 

 vain for a vegetal support and swim to the last before settling down 

 on the slide. Under natural conditions they very likely settle 

 down after a much shorter time ; the number of empty, but quite 

 fresh-looking shells which are found in the gatherings is such that 

 one might expect to find a good number of swimming larvte also, 

 but these are in fact exceedingly rare. This however might easily 

 be explained by a very short swimming period. If that period is 

 lengthened, one might suppose that the special secretion, already 

 prepared when leaving the old shell, and which represents the 

 material for the new one, had been gradually lost. . 



Such is, as far as I could observe it, the course of events in the 

 total transformation of Folliculina. Some minor facts concerning 

 the vacuoles or lacunae, the nucleus, which generally becomes 

 temporarily longer and often double, the coloured grains, etc., 

 might be referred to ; I will only add a few words concerning the 

 possibility of conjiigation. 



Sahrlage, on page 169 of his work, writes as follows : " The 

 process of conjugation would presuppose the existence of free- 

 swimming adult Folliculin^e, which however have not yet been 

 proved by any observer to exist." Now we have seen that such 

 Folliculina^ do exist, and the possibility of coiijugation is therefore 

 no longer in doubt, though I have never seen any indication of the 

 fact. 



Adult State without a Shell. 



Much more frequently than vermiform larvae are found naked 

 specimens possessing the general characters of t]ie shell-bearing 

 type, and provided with lobes and a well-developed peristome. So 

 far as can be inferred from their general appearance, it is probable 

 that these specimens have been accidentally dislodged from their 

 shells ; perhaps, also, some of them may have been incited by 

 abnormal circumstances to leave their envelope suddenly, without 

 preparing for a swimming vermiform state. These specimens are 

 mostly found retracted (fig. 16), often wounded or lacerated; when 

 transferred to the slide in clear water they may live for days, but 

 hardly ever depart from their retracted condition. In one case. 



