Dr. C. A. Kofoid on Platydorina. 545 



The colours of Platydorina are quite as striking as those of 

 related forms. The cells, which are imbedded in the trans- 

 parent gelatinous matrix of the colony, are a bright chloro- 

 phyll-green, and each has, as a rule, a red stigma or eye-spot 

 of unusual brilliancy. 



The substance in which the cells of the colony are imbedded 

 is similar in appearance to that in Eudorina. It is a trans- 

 parent colourless substance of considerable consistency, showing 

 in the living condition, as a rale, no trace of differentiation. 

 The gelatinous nature of the substance is shown by the great 

 numbers of bacteria which swarm within it in moribund 

 specimens. Colonies killed in formalin and stained in Dela- 

 field's hematoxylin exhibit a difference in the intensity of 

 coloration, indicating the presence of a denser peripheral 

 layer or sheath 3-4 [x in thickness (PI. VII. figs. 1, 4,p.sh.). 

 This is apparent along the edges of the colony and presumably 

 extends over its faces. In several living colonies a granular 

 differentiation of this outer layer was noted about the margin. 

 This sheath is similar to that of Eudorina and Pleodon'na, 

 but shews no trace of the concentric layers so prominent in 

 Pandorina. 



One of the most characteristic features of the colony is the 

 presence upon the posterior border of 3 or 5 projections or 

 tails, which are merely extensions of the sheath. Colonies of 

 16 cells have but three tails, while those of 32 cells have 

 uniformly five. These projections are bluntish finger-like 

 processes without structural differentiation, tapering some- 

 what to a rounded or pointed end. Occasionally the outer- 

 most pair, and more rarely the inner one, are slightly divergent. 

 In the 16-cell colony there are two latero-posterior tails and 

 one median one (fig. 2), the former being better developed 

 and measuring 15 to 20 /x. in length. The median tail is 

 variable in length, being sometimes a mere rudiment appearing 

 on a slight elevation on the margin. Its average length is 

 about one third that of the adjacent pair, though it occasionally 

 attains two thirds their length. The latero-posterior tails are 

 upon each side of the colony directly behind the marginal 

 row of cells, while the median tail is midway between the 

 central rows. In the 32-cell colony (fig. 1) there is, in 

 addition to the three tails above noted, another pair which 

 may be designated as the lateral pair. These tails are slightly 

 divergent, arising at the outer posterior angles of the marginal 

 row of cells, between the last transverse quartet and the last 

 sextet of cells. They are from 10 to 15 \i in length and are 

 often of the same size as the median tail of the colony. The 

 other three tails occupy the same position with respect to the 



