345 
Notes on British Flagellates. I — IV. 
of them being plainly visible ; liberation was obviously not far off in 
such cases, but attempts to follow up the further course of events 
proved unsuccessful owing to the death of the organisms under 
conditions of culture. Stages were also observed in which the 
mother-envelope had lost its well-defined outline and was evidently 
becoming mucilaginous, and it is the more probable that this 
represents the mode of liberation of the daughter-individuals as 
empty envelopes from which the latter might have escaped by 
splitting were never observed. From all this it appears safe to 
assume that reproduction of Isococcus takes place by division in the 
resting condition, the planes of the first two divisions at least being 
longitudinal and the fully-developed daughter-individuals becoming 
free by gelatinisation of the envelope of the mother. Most division- 
stages were always observable in the morning, so that division 
probably takes place over night, the products being liberated towards 
the end of the following day. 
In a few cases very small (diameter 12//,) individuals of Isococcus 
were encountered in active movement, but provided only with a 
very delicate envelope. These probably represent products of recent 
divisions that have been liberated prematurely before they were 
fully differentiated; in all other respects they agreed with the 
normal organism. It appears as though the young individuals are 
more commonly oval than spherical, but that they tend to assume 
the latter shape as they increase in size, since a considerable 
percentage of the larger specimens are almost spherical. 
As regards the systematic position of Isococcus the general 
organisation of the cell stamps it as a member of the Volvocales 
although the chloroplast approaches a more nearly spherical form 
than is usual in that group. The only green member of Volvocales 
with a simple envelope hitherto described, is Coccomouas', but this 
differs from the form under consideration in many respects—most 
markedly in the fact that the individual within the envelope is not 
naked, but is clothed by a cell-membrane. Other differences are 
seen in the single cilial aperture of Coccomouas, in the presence of 
a single pyrenoid in the latter, and in the fact that the envelope gets 
burst open after division. As a matter of fact Coccomouas is merely 
a Chlamydomouas which has acquired an independent envelope, 
whereas Isococcus constitutes a parallel to Trachelomouas among the 
Euglenineae and Chvysococcus among the Chrysomonadineae. Its 
naked protoplast places it on a lower level than Coccomouas and 
relegates it to the Flagellate side of the Volvocaceous series. Its 
1 Cf. Wille, in Engler and Prantl, Die naturl. Pflanzenfam. I Teil, 2 
Abt., 1890, p. 40, fig. 22, M, N. 
