Volvox and Associated Algae from Kimberley. 487 



in embryo colonies before escape, but are entirely absent in the adult. 

 At certain stages of inversion of the embryo in V. gigas, as described 

 above, relatively stout protoplasmic connections between the cells 

 became obvious in those parts of the embryo which are being stretched, 

 and are certainly present throughout, although owing to the small size 

 of the embryo and the close packing of the cells, except at the edges, 

 they are not distinguishable. Now it must be remembered that the 

 cells of the young embryo are not enclosed in a common membrane, 

 but lie in close contact with one another. During inversion the cells 

 act in concert with one another, but each is at the same time altering 

 its shape and must to some extent act independently ; while some are 

 being compressed, others are in a state of great tension, tending to 

 separate from one another. Obviously, since the globoid inverts as 

 a whole, the connection between the component cells must be very 

 intimate. It would appear that this is obtained by the presence of 

 protoplasmic connecting strands, which therefore play an important 

 role in the process of inversion, on completion of which they become 

 functionless and are withdrawn, one only surviving here and there 

 to a later stage in development. A further advance in complexity 

 of structure is reached by those species which retain the protoplasmic 

 connections throughout their life, e.g. V. aureus, while the members 

 of the globator group have progressed yet a step further, since in these 

 the connections develop as the colonies mature, reaching their maxi- 

 mum thickness when the reproductive cells are developing. 



Development of the Embryo subsequent to Inversion. The embryos 

 are very small at the time of inversion (e.g. 58 x 66 p., 71 x 53 /x) and 

 enlarge considerably before birth (Plate XXVI, E). The component 

 cells very soon begin to separate from one another, enlarging as they 

 do so, while the gonidia now become very distinct from the somatic 

 cells (Plate XXVI, E, and Plate XXX, D), their diameter at this 

 stage being nearly double that of the latter ; for example, in an embryo 

 measuring 77 x 87 /x the vegetative cells measured 3 to 4 /*, the 

 gonidia 5 to 6 /z. As the embryo develops the proportion between 

 the two types of cells remains approximately constant, until the 

 somatic cells reach their maximum size, after which the gonidia still 

 continue to grow until finally they are three times the diameter of the 

 vegetative cells, or even more. Young oospheres are considerably 

 smaller and increase in size more slowly, while the majority of the 

 antheridium mother-cells do not grow much larger than the somatic 

 cells until late in development (Plate XXVIII, C), although in some 

 male colonies a few here and there enlarge similarly to the gonidia 



