Volvox and Associated Algae from Kimberley. 495 



(fig. 4, B). The microphotograph reproduced in Plate XXXI, C, shows 

 a mature colony from which the equatorial embryos have already 

 escaped, the respective pores of escape of two of them showing clearly 

 at the two sides near the equator. The posterior embryos, of which 

 three are seen, have continued to grow after the others had escaped 

 and nearly fill the posterior half of the parent. The membranes 

 surrounding the embryo colonies show clearly, and the inner mem- 

 brane of the parent can just be distinguished above the latter and in 

 the anterior part of the coenobium. The colony had been treated 

 with methylene blue and was photographed free on the slide to avoid 

 undue distortion. The same colony, unstained, appears in the 

 group (Plate XXXI, A) just above. The position of the embryos 

 between the two membranes in V . africanus, as in F. gigas, probably 

 accounts for the lateral compression and elongated shape often 

 characteristic of young embryos ; but in the former species they 

 attain a very much greater size in proportion to the parent than in 

 the latter, and soon become wider than the peripheral zone, hence 

 the great distortion of the inner membrane. 



Inversion of Embryo Colonies. Inversion figures are not abundant 

 in the material, but in proportion to the number of embyro coenobia 

 examined they are far more numerous than in F. gigas, and what 

 there are are excellent, particularly in the iodine-fixed material, 

 showing no appreciable distortion. Probably the process is a much 

 lengthier and more complicated one than in that species ; this was to 

 be expected from the fact that the cells are far more numerous in 

 proportion to the size, and further, that the gonidia are already large 

 before inversion takes place. On the completion of cell division, the 

 gonidia, particularly the two equatorial pairs, are large and project 

 far inwards from the peripheral layer of somatic cells. In one 

 inverting embryo the size of the gonidia varied from 9 //, at the 

 posterior (phialoporic) end to 16 fj, at the equator. 



So far as could be made out from the available material the stages 

 in inversion are as follows : 



There is a well-marked preparatory stage characterised by the 

 infolding of the four lobes of the phialopore and more or less extensive 

 denting such as is seen in V. Rousseletii and F. capensis, etc. (fig. 5, 

 A, B). At this stage the vesicle sometimes has a curious dumb-bell 

 shaped appearance. The phialopore enlarges considerably without 

 the lip becoming straightened out, and a constriction appears some- 

 where between the equatorial and the posterior gonidia ; the upper 

 (outermost) part, still double, folds back (fig. 5, C), and the " hat " 



