262 On Pleurocystis cu(^aoti, Hesse. 



cells of a filament of tlie alga Spirogyra to one another, and 

 is affected by siniilai' stains (e. g. Bismarck brown). It is 

 unaffected by dilute (1 °/q) acids {cf. tiie cysts), but the indi- 

 viduals can be made to part from one another by pressure on 

 the coverslip, thougii not without rupture of the cuticle — 

 which is evidence against their permanent fusion into one 

 organic individual. 



Summary. 



(1) Pleurocystis has established claims to be considered an 



independent genus. 



(2) It occurs in the same host {Helodrilus longus) both in 



England and France. 



(3) The individuals are in lifelong diploidal association, 



and not merely at tiie period of conjugation, as was 

 supposed in }[onocystis magna, since the nuclei show 

 no signs of division, and it is improbable that seven 

 presumed conjuganis should be in the same initial 

 stage. 



(4) Tiie diploids show a caudal formation^ but whether this 



is due to Euglenoid movements or oncoming cyst 

 secretion, or is an artefact, is uncertain. 



(5) I have attempted to set forth reasons for believing that 



diploidal association commences at the posterior extre- 

 mity of the individuals. 



(6) The animals attain a greater magnitude than Hesse 



asserted. 



(7) There is an anterior organ of attachment. 



(8) The partners are firmly but not inseparably attached by 



an adhesive secretion, and are not permanently fused 

 into one individual. 



Eeferences. 



BoSANQtTET. (1894). " Notes on a Gregarine of the Earthworm {Lum- 



bricus herculetis)." Quart. Journ. Microsc. Sci. xxxvi. p. 421. 

 BuTSCHXi. (1882). Brouu's ' Thierreich,' i. Abt. i. Leipzi-r. 

 Cecoxi. (1903). " De la Sporulation de la Monucystis ayilU^ Stein." 



Arch. d'Auat. 31icrosc. v. p. 122. 

 CufiNOT. (1900). " liecherches sur I'^Tolution et la conjugaisou dea 



Gregarines." Arch. Biol. xvii. p. 581. 

 Hesse. (1909). "Contribution a I'^tude de.s Monocystid^es des Oligo- 



chetes." Archives de Zool. experim. iii. p. 27. 

 Schmidt. (1854-5). " Beitrag zur Kenutuiss der Gregarinen und 



deren Eutwickelung." Abhand. herausg. von der Sencken- 



bergischen. NHturforsch. Gesellsch. i. p. 168. 



J 



