262 On Pleurocystis cuénoti, Hesse. 
cells of a filament of the alga Spirogyra to one another, and 
is affected by similar stains (e. g. Bismarck brown). It is 
unaffected by dilute (1 °/,) acids (ef. the cysts), but the indi- 
viduals can be made to part from one another by pressure on 
the coverslip, though 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 the period of conjugation, as was 
supposed in J/onocystis magna, since the nuclei show 
no signs of division, and it is improbable that seven 
presumed conjugants should be in the same initial 
stage. 
(4) The diploids show a caudal formation, but whether this 
is due to Huglenoid 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. 
REFERENCES. 
BosanquEt. (1894). “ Notes on a Gregarine of the Earthworm (Zwm- 
bricus herculeus).” Quart. Journ. Microsc. Sci. xxxvi. p. 421, 
Bitscui. (1882). Bronn’s ‘ Thierreich,’ i. Abt. i. Leipzig. 
Cxconr. (1903). “De la Sporulation de la Monocystis ayilis, Stein.” 
Arch. d’Anat. Microsc, v. p. 122. 
Cutnot. (1900). “ Recherches sur ]’évolution et la conjugaison des 
Gregarines.” Arch. Biol. xvii. p. 581. 
Hesse. (1909). “ Contribution a l’6tude des Monocystidées des Oligo- 
chétes.” Archives de Zool. experim. iil, p. 27. 
Scumipt. (1854-5). “Beitrag zur Kenntniss der Gregarinen und 
deren Entwickelung.” Abhand. herausg. von der Sencken- 
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