30 West & West . — Observations on the Conjugatae. 
it is better regarded as a sub-family of the Zygnemaceae, as 
Pyxispora has the same method of formation of its spores, 
although the chromatophores are similar to those of Zygnema . 
These plants may occur as solitary cells, or they may be 
filaments which at some or all periods of their existence more 
or less easily dissociate into the separate cells of which they 
are composed. The genus Gonatozygon may be taken as an 
illustration ; it is sometimes found in long filaments of about 
thirty or more cells ; but on being subjected to the least dis- 
turbing influences these filaments break up, and in some species 
of the genus the filamentous condition is rarely attained. 
There is a tendency in many of the small species of Cos- 
marium , very noticeable in C. moniliforme and C. Regnellii , 
to assume a filamentous condition, and this may have induced 
Rabenhorst 1 to place C. pygmaeum under Sphaerozosma. We 
have also noticed this tendency in Euastrum binale (cf. Fig. 38). 
In Micrasterias foliacea , a representative of a genus the species 
of which normally occur as solitary plants, this filamentous 
condition has been attained by a remarkable degree of 
specialization of the polar lobes of the semi-cells, which 
possess an arrangement of apical teeth which interlock so 
firmly with those of the adjoining cell, that the connexion 
is too rigid to allow of hardly any flexibility in the filaments. 
A filamentous condition of the genus Mesotaenium (which is 
generally unicellular) is found in the Arctic plant named by 
Berggren Ancylonema N ordenskioldii. The filaments of Hyalo - 
theca dissociate into separate cells just prior to conjugation, 
and the dissociated cells remain imbedded in a mucus derived 
from that which surrounded the original filaments. Conjuga- 
tion is very soon general throughout the mass, as can readily 
be seen in a conjugating example of H. dissiliens. The frag- 
menting of the old filaments into individual cells is well known 
as a method of reproduction in some genera of Zygnemaceae. 
It can therefore be considered that a strictly filamentous 
condition is of no essential importance to the life of the 
Conjugatae. 
1 Flor. Europ. Algar. Ill, p. 150. 
