Volvox and Associated Algae from Kimberley. 483 



The somatic cells (fig. 2, A, B) are practically spherical, sometimes 

 showing a very slight anterior projection ; they lie below the surface 

 membrane suspended in the non-staining vesicle enclosed by the 

 lenticular cell membrane. The extensive lobed chloroplast lines 

 the whole wall except for a small area at the apex ; there is a large 

 basal pyrenoid from which several smaller pyrenoids later separate 

 off, and a central nucleus; with methylene blue the whole proto- 

 plast stains blue, the nucleus and pyrenoids more deeply than the 

 cytoplasm. In the anterior part of the colony each cell contains a 

 large lenticular orange-red eyespot (3 to 4 /JL in diameter), which, as 

 in all other colonial members of the Volvocinae as yet examined, 

 occupies a definitely orientated position in the cell, i.e. it lies on that 

 side of the cell farthest from the anterior pole. The eyespot is 

 usually rather low down, about midway in the cell (fig. 2, A). 



The cilia are inserted separately, diverging slightly before they 

 reach the surface membrane. No indication whatever has been seen 

 of protoplasmic connections in mature coenobia, although in colonies 

 of V . Rousseletii in the same material they showed clearly. In young 

 unborn daughters, however, here, as in V. africanus, occasionally a 

 connection may be seen between adjacent cells. Such connections 

 are rare and at the best of times obscure, at any rate in preserved 

 material (but see later, in connection with inversion). 



Reproduction. The reproductive cells are variously distributed ; a 

 coenobium may produce only gonidia which develop into embryo 

 colonies (Plate XXVI, C, D, E), only male or female organs (Plate 

 XXV, B 1 and 2), or all three. As a rule, however, the sexes are 

 separated, sperm bundles rarely occurring except in exclusively male 

 coenobia, although mixed colonies producing daughter colonies and 

 oospheres are common (in one case over 70 embryos and about 43 

 oospheres were counted in a single colony), and reach a large size 

 (Plate XXVI, B, and Plate XXX, B). Purely female colonies, on the 

 other hand, are little larger than the male colonies, but usually rounder 

 in shape. The four types of colonies, i.e. asexual, male, female, and 

 mixed, and their relative shapes and sizes, are well illustrated in the 

 group figured on Plate XXV, D. In this group, too, a few very 

 young colonies are included. 



(a) Asexual. As already stated, the gonidia are differentiated 

 early, but undergo a prolonged period of enlargement before division 

 begins (cf. Plate XXVI, A). Colonies of over 1 mm. diameter in 

 which the gonidia show no sign of division are often seen. 



Structure and Development of the Gonidium. When young the 



