134 
B. Millard Griffiths. 
the pyrenoid, dividing it into two parts, each part having two 
complete lobes of the original chloroplast (Pig. 14, B, C. I, J). 
The incisions at the extremities of the lobes play an important 
part, for by their increasing depth, the four lobes of the new 
chloroplast are formed. 
Before this takes place however, the original cell-membrane 
becomes invaginated posteriorly in the median line (Fig. 14, E). 
The invagination gradually deepens and passes between the two 
halves of the chloroplast (Fig. 14, F, G, K), so that the cell becomes 
divided into two lobes, joined together at the ciliated end. 
The cilia increase in number from four to eight. The new 
cilia do not always appear at the same time. Specimens were 
noted with five (Fig. 14, E), six and seven full-grown cilia. The 
appearance of the cilia seems irrespective of the state of the 
division of the cell, but no case was observed in which they arose 
before the division of the pyrenoid. 
The nucleus usually lies in the cup of the chloroplast, about 
half-way up, on the side of one of the lobes (Fig. 13, C, Fig. 14, G). 
It is often difficult to observe in the division stage, but it was fully 
made out in two cases. It divides into two, and these take up 
positions as seen in Fig. 14, D. 
The fission of the cell is continued until two separate and 
rather elongated organisms are found. These proceed to repeat the 
same cycle of growth and division. 
No amoeboid alterations in the shape of cell were observed 1 ; 
the only change noticed was the greater stoutness of the cell as the 
period of fission approached. 
No encysted state was observed. 
Pyramimonas delicatulus is exceedingly susceptible to adverse 
conditions. Attempts to make cultures either in the original water 
or with Knop’s solution were unsuccessful. If the temperature 
rose above 9°C, the organisms were killed and partially disin¬ 
tegrated. Keeping in wide glass tubes for more than a few days 
was equally fatal, even at a temperature of 6 or 7°C. 
Effects of Formalin. Weak solutions of formalin are so widely 
used for fixing and preserving algae that some remarks upon the 
effects produced on Pyramimonas may be of value. All attempts at 
preserving this alga in solutions of 4%, or under, proved disastrous. 
1 In this respect Pyramimonas appears to differ from the other 
members of the Polyblepharidea. Consult Teodoresco on 
Dunaliella, Beihefte zum Bot. Centralblatt. Band XVIII., 
Abt. I., Heft. 2, 1905, p. 217. 
