488 Annals of the South African Museum. 



(Plate XXVIII, A, B). The relative sizes of recently inverted and 

 mature embryo colonies can be seen in Plate XXVI, E. 



In addition to the typical ellipsoidal embryos composed of over a 

 thousand cells there are often scattered among them others, usually 

 rounded, composed of far fewer cells, in some cases as few as 64, but 

 more often 128, 256, etc. ; in these the majority of the cells enlarge 

 proportionately more than in typical embryos, e.g. in one such colony, 

 already free, measuring 58 //, in diameter and composed of 128 cells, 

 the majority of the cells measured 10 fj,, while a few at one end were 

 smaller. Such " dwarf " colonies appear to be male colonies in which 

 nearly all the cells function as antheridium mother-cells ; the develop- 

 ment of the sperm bundles, however, does not take place until after 

 escape, and such small males are rare compared with the larger egg- 

 shaped male colonies. The small colony shown in Plate XXV, C, 

 contains young male colonies of this type and a few oospores. 



(b) Sexual. (1) The male reproductive cells are nearly always 

 found in exclusively male colonies, which are slightly smaller than 

 the purely female colonies and which often become markedly egg- 

 shaped as the sperm bundles develop (Plate XXV, B), or more rarely 

 they may be such rounded dwarf colonies as are described above. 

 Occasionally, however, sperm bundles have been found in female or 

 mixed colonies, where one or two sperm bundles were scattered among 

 the developing oospheres. As, however, such bundles are small and 

 easily mistaken at low powers of magnification for oospheres just 

 beginning to enlarge, it is quite possible that they may be of more 

 common occurrence than would appear to be the case. 



In the male colonies all the cells in the posterior half become 

 antheridium mother-cells (Plate XXIX, A), a small anterior portion 

 remains somatic, while between the two lies a zone where male initials 

 and somatic cells are mixed (Plate XXVIII, C). Thus some three- 

 quarters or more of the total number of cells in the male colony may 

 develop into sperm bundles. 



The antheridium mother-cell varies enormously in size it may 

 divide on reaching a diameter of 18 to 20 /x, or division may be delayed 

 until it is more than double that size, i.e. as large or nearly so as a 

 mature gonidium. The number of divisions undergone depends on 

 the initial size of the cell ; most often it is 5, resulting in a bundle of 

 32 sperms, but bundles of 16 and 64 occur, while in many male colonies 

 scattered among these smaller sperm bundles are others very much 

 larger, containing a much greater number of spermatozoids 256, 512, 

 or possibly even more. The latter are not unlike sperm bundles of 



