]6 ANNIE PORTER 



In stained préparations Fantham (I, 1908, p. 45) has already 

 set forth a method of determining the validity of transverse 

 division of Spirochaetes by counting the number of chromatin 

 masses in the daughter forms of an almost divided *S^. haïbianii 

 (Quart. Jour. Microsc. Soi., Vol. 52, PI. III, fig. 19). The num- 

 bers of chromatin masses in each daughter form were thirty 

 eight and forty-three respectively. which approximate to the 

 numbers seen in many spécimens. 



B. Encystment, etc. 



Encystment of S. haïbianii has been recorded by Perrim 

 (1906) but other workers hâve not observed this. In fact, 

 Swellengrebel (1907) states that protoplasmic globules 

 within the outer zone of the style of Ostrea are really the 

 structures that Perrin calls cysts. 



According to Brasil, encystment of parasites should be sear- 

 ched for at the reproductive season of the host harbouring 

 them.Tliis has been done by Fantham (I, 1908) who states that 

 he has not seen encystment. This year I carefully investigated 

 many Anodons, whose gills were crowded with Glochidia as 

 well as Anodons whose ovaries contaired ova in ail stages 

 of development. In this condition one would expect the host 

 to react upon the parasites, and encystment of the latter 

 should follow as a matter of course. Though I hâve examined 

 many infected Lamellibranchs, I can only confîrm what Fan- 

 tham said, for I hâve never seen encystment of 8. anodontae. 



On one occasion I saw M'hat I believed would be encystment 

 (figs. 25 to 28). An actively moving parasite (fig. 25) suddenly 

 threw itself into coils about the middle of its length (fig. 26). 

 This central mass tightened, forming a clumsy coil (fig. 27). 

 The membrane of this parasite remained comparatively still 

 and was somewhat relaxed. The organism then resembled a 

 form figured by Perrin (1906), in which both ends were free, 

 but a globular (( cyst » had begun to form at the centre of the 



