286 Lang . — The Prothallus 
prothalli investigated : but the striking fact results from the 
detailed study of complete series of sections of six prothalli 
and the external examination of another, that a practically 
complete separation of male and female sexual organs on old 
prothalli of similar size and form may occur. Of the seven 
prothalli six were female and only one male. No archegonia 
were found on the latter, but on two of the female prothalli 
a few antheridia were seen among the much more numerous 
archegonia. In the absence of continuous observations on 
developing prothalli it was impossible to be certain whether 
the same prothallus passes through a male and a female stage, 
or if at an earlier stage both kinds of sexual organs do not 
co-exist h 
The archegonia and antheridia occupy corresponding 
positions : both are confined to the upper surface of the 
prothallus. In the specimen represented in Fig. 2 , the arche- 
gonia were scattered over the slightly projecting cushion, the 
youngest being found nearest to the edge, a distribution that 
is explained by the marginal growth. In older prothalli the 
central region bore only old and often almost unrecognizable 
sexual organs, while the functional and developing archegonia 
and antheridia were found near the margin, the part of the 
cushion on which they were situated projecting as a more or 
less prominent ridge. The position of this ridge will be 
evident from Figs. 8 and 9, which represent vertical sections 
across the margins of the prothalli shown in Figs. 4 and 3 
respectively. As the figures show, the central region of the 
upper surface of these prothalli bore only obscure remains 
of antheridia or archegonia, while on the marginal ridge 
a succession of these organs can be traced, the youngest being 
nearest to the marginal groove. In the case of the male 
prothallus (Fig. 3) this ridge was only present within the 
lateral margins, while in the largest female prothallus (Fig. 4) 
the appearance of a vertical section of either end was in- 
1 Bruchmann’s observations (loc. cit., 1898) show that as a rule archegonia and 
antheridia occur together on the prothallus. He does not mention any cases of 
their separation in old prothalli such as those described in the text. 
