260 Mr. W. H. Leioli-Shaipe on 



careful consideration. to the matter ot tlie clainis of y^emato- 

 cystis and Pleurocystis as independent genera, I have come 

 to the conclusion that the characters of my specimens agree 

 in the main with those diagnostic of Pleurocystis except in 

 regard to a small discrepancy as to size, Hesse states that 

 Pleurocystis is 2 mm. long and ^eniatocystis 5 mm., whereas 

 my specimens are of the lengtii of 4-5 mm. If the animal is 

 as rare as Hesse implies, it is possible that it may attain 

 dimensions greater than that mentioned by him, or, again, 

 that an English variety may be larger than the French one 

 which he found in and around Daupliine. There exists, as 

 far as I can ascertain, no previous record of Pleurocyblis 

 occurring in the British Isles, though it has possibly been 

 found and confused with the presumed conjugation stage of 

 Monocystis magna, which Hesse has now determined is not 

 a conjugation but a life-association into diploids, thereby 

 deciding him to alter its name to Nematocystis magna. 



The statement of Ceconi (1903) that in Monocystis agilis, 

 at any rate, each conjugant separately forms a cyst around 

 itself, which afterwards coalesces with that of its partner, 

 was scouted by Cuenot. Such is not true at any rate for 

 Pleurocystis, where the double (cuticular) separation between 

 the individuals is never hroken down. The cuticle exhibits a 

 network of fine striations, and as the cytoplasm shrinks away 

 from it by plasmolysis, it may peihaps have been mistaken 

 for a cyst. Some of the specimens were ruptured, and others 

 easily became so at the slightest touch. The endoplasm was 

 plentifully stored with paramylum (or paraglycogen). 

 Specimen A, which is also the largest, being 1 mm. longer 

 than any other diploid, is markedly difi'erent from the rest. 

 It exhibits a kind of caudal formation, as though it had been 

 killed while making Euglenoid movements; further, the 

 cytoplasmic contents extend right to the posterior extremity, 

 and are more densely granular. Conversely, the other 

 specimens present a normal specific outline, the cytoplasm is 

 withdrawn from the posterior extremity as though shrinkage 

 was occurring previous to cyst-secretion. From these obser- 

 vations I infer that A is an earlier, and possibly the earliest, 

 stage of diploid association, and that the other figures represent 

 subsequent stages. The figures of no other observer represent 

 any such caudal formation. 



Though I have figured a nucleus in two individuals, these 

 were not apparent through the cytoplasm ; but, upon rupture 

 of the cuticle, when the contents become extruded the nucleus 

 is plainly visible. The nucleus is situated about hallway 



