MIDLAND NATURALIST. 7 
various stages are shown in the plate in figs. 1-11. There was 
no need of hunting for the intermediate stages as nearly every 
particle of plankton contained them all, and often the field of a 
one-eighth microscopic objective with one inch ocular presented 
a complete series of stages of spore formation. 
Following is a description of the process of the formation of 
the resting spore. Two semicells of the desmid, Cosmarium 
bioculatum separated from one another as the plants usually do 
in the formation of zygospores, only one individual, however, 
being engaged in the process. The protoplasm from each semi- 
cell emerged and formed a transparent globular vesicle. This 
vesicle gradually became invested with a thick cell wall on reaching 
full size. The two chromatophores with nuclear bodies each with 
a small body in it resembling a nucleolus on entering the vesicle 
took up positions at opposite pole of the vesicle only fusing their 
protoplasm along a thin median band, thus seeming at least in 
the early stages of the spore formation to maintain their individ- 
uality in the spore. The whole spore as also the vegetative stage 
of the desmid was invested with a thick mass of mucilaginous 
material. This fact was beautifully demonstrated in staining 
with diluted Delafield’s Haematoxylin bringing up in alcohol 
counterstaining with Magdala Red and mounting in Venetian 
turpentine or balsam. The preparations thus made showed the 
cell wall of the desmid as also of the vesicle a rather deep purplish 
blue, the cell contents especially the chromatophores a bright red, 
and the mucilage coat pale lilac to purple. Thus it was easy to 
prove that one and only one desmid was engaged in the process 
of spore formation and therefore that it was not conjugation. 
Other preparations, using Magdala Red alone, showed the cell 
contents more clearly as the cell wall could be bleached to any 
degree of paleness or the stain quite removed by measured exposure 
to sunlight. Though thousands of the spores of Cosmarium biocu- 
latum were examined under various conditions of staining and 
particularly im the study of the live material not a single case was 
found where more than one individual was noticed in the formation 
of the spore. The method of the formation of the spore is then 
a purely asexual one, unless the union of the contents of one semi- 
cell of an individual with those of its other half or of the other 
semicell can be considered a sexual process. The contents of each 
semicell of an individual can of course be supposed to become a 
gamete to the other half, and the resulting spore could in this sense 
be considered a zygospore by a degenerate form of conjugation. 
