Folliculina holtoni (S. Kent). 307 



water, Wright, as well as Claparede and Lachmann, would have 

 been able to present their statement not as a possibility, but as an 

 undeniable reality. 



General Chaeactees. 



The genus Folliculina is characterized by the possession of a 

 shell which, in F. holtoni, measures about 200 /a in length, is 

 pyriform in shape, and at the same time very much compressed 

 dorso-ventrally. It looks very nearly the same as the shell of 

 Vaginicola longicollis, and, like this latter, adheres very firmly to 

 the substratum. The anterior part is somewhat elevated in a neck- 

 like prolongation, and opens in a circular aperture (fig. 6). This 

 shelly which has been generally described as chitinous, is in 

 reality quite different from that of Vaginicola, and rather might 

 be considered as consisting of hardened mucilage. We shall later 

 on refer again to the structure of the shell, and also to the cause 

 of its coloration, which is of a bluish bottle-green like the body 

 itself. 



The animalcule, which hardly fills more than half the shell, 

 differs very much in appearance when seen in a state of expansion 

 (figs. 1, 4, 5, 7), or retracted (fig. 8). Completely expanded, the 

 body is fusiform, attached to the bottom of the shell by its posterior 

 extremity, while anteriorly it stretches in a very extensible neck- 

 like prolongation, and finally expands in two long wings or lobes, 

 whose rim carries the peristomial wreath. 



The particular structure of the peristome in Folliculina, and the 

 course of the adoral line along the lobes and inside the " vestibulum " 

 have been the subject of many investigations. Claparede and 

 Lachmann, Stein, Mobius did their best to understand its com- 

 plexities. More recently Sahrlage has done the same in a more 

 exhaustive study (p. 153-155), and I would refer those interested 

 to his work for details, satisfying myself with reproducing here 

 the lines which Delage (" Traite de Zoologie," p. 463) devotes to 

 the subject : — 



" Folliculina (Lamark) may be considered as being derived from 

 a Stentor whose pseudostome would be developed into two lateral, 

 very extended wings, whilst the medial anterior and posterior parts 

 would have remained at the same level. The result is that the 

 peristome has acquired the form of a deep funnel, split anteriorly 

 and behind. The adoral zone follows the free border all along, 

 begins anteriorly, continues along the free border of the right 

 wing, descends to the base of the posterior sinus (less deep than 

 the anterior), ascends along the left wing, and finally descends 

 towards the original point of departure ; but, instead of joining it, 

 it plunges spirally into the buccal vestibulum, where it describes 

 one and a half turns, and finally enters the mouth." 



y 2 



