Volvox and Associated Algae from Kimberley. 481 



gonidia are quite clearly differentiated from the somatic cells at a 

 very early stage, certainly very shortly after inversion of the embryo 

 colony, and continue to enlarge with the somatic cells within the 

 parent and after birth, but do not begin to divide until the colony 

 has reached a large size, usually over 1 mm., when the gonidia may 

 be as much as 44 to 49 JJL in diameter ; and (4) the structure and dis- 

 tribution of the sperm bundles ; in the posterior part of the male 

 colony all the cells become antheridium mother-cells, i.e. they are not 

 mixed with somatic cells ; the size of the antheridium mother-cell, 

 and consequently the size of the resultant sperm bundle and the 

 number of spermatozoids composing it, all vary greatly. 



Membranes and Cell Structure. The membranes (fig. 1) are similar 

 in arrangement to those of F. tertius Meyer and F. africanus West. 

 In the recently inverted embryo the polygonal (usually hexagonal) 

 protoplasts are in contact, but begin at once to separate from one 

 another. At birth and for some time after, treatment with methylene 

 blue shows the cell membranes as more or less hexagonal in outline 

 (fig. 1, B) ; as development proceeds and the cells become further apart, 

 each protoplast is seen to be enclosed in a wide, lenticular membrane, 

 which is in contact with the outer limiting membrane over a circular 

 or elliptical area above the protoplast (fig. 1, A, D). The membranes 

 of adjacent cells are at first in contact, but in adult colonies they may 

 be completely isolated from one another (fig. 1, E, K). Even in this 

 stage, however, it is sometimes possible to distinguish faint hexagonal 

 markings on the outer membrane of the colony (fig. 1, J). The spaces 

 between the cell membranes stain faintly purple, while the membranes 

 themselves are deep reddish purple. The appearance after treatment 

 with methylene blue, as seen in surface view at different focal depths, 

 is shown in fig. 1, F-H, while J and K show corresponding views from 

 an older colony. 



In young colonies the peripheral gelatinous layer is wide, and more 

 so in the posterior than in the anterior region of the colony, about 

 60 to 70 IJL at the anterior, 70 to 80 ^ at the posterior pole (fig. 1, A) ; 

 as the colony gets older it becomes narrower and less regular (fig. 1, C), 

 varying considerably in one and the same colony. It is bounded on 

 the inside by a purple-staining membrane, similar to but more delicate 

 than the outer membrane. The fluid filling the central hollow 

 appears to be slightly mucilaginous, but shows no definite structure. 

 The daughter colonies develop within the much enlarged gonidium 

 walls, lying between the inner and outer membranes ; hence, prob- 

 ably, the elongated shape of the young embryos (fig. 1, E). 



