ON ACTINOCOCCUS AND PHYLLOPHORA. 171 



germinating spores of Actinococcus subcutaneus. This parasite can only 

 enter the host when the male (or the female 1) organs of the latter are 

 present. It has been known to the author for some time that the 

 antheridial cavities of Phyll, Brodiaei often accompanied the presence 

 of Actinococcus subcutaneus, but only daring the last year has it become 

 possible to explain definitely the significance of this appearance. 



As the presence of the antheridial cavities is so intimately associated 

 with the relationship of the two red Algae which form the subject of 

 this paper, it might be useful to recall the structure of the former 

 (2, p. 29). 



The antheridia of Phyll. Brodiaei are developed in the cortical layer of 

 the spermophores, the latter being shoots more or less modified tempora- 

 rily for the production of the male organs (Figs. 4, 5). They are slightly 

 flattened near the lighter coloured apex, attaining a length of about 

 3 mm., being rarely broader than 05 mm., and they are borne on the 

 apical margin of the flattened vegetative thallus. In the cortex of 

 such a spermophore, close to its apex and not further down from it 

 than 1*0 — 1*5 mm., we find the small cavaties which contain the 

 antheridia. These cavities are flask-shaped and communicate with the 

 exterior by a small ostiole. Their height is 24 — 34 jj., their breadth 

 about 20 /.i. From the flat bottom of the flask-shaped cavity arise a 

 number of 2, 3, or even 4-celled antheridia, which produce the single 

 male cells or spermatia, at their apex (Fig. 5). The spermatia pass 

 out of the cavity through the ostioles, which measure about 6 — 10 fx 

 across. 



It is not necessary to describe the carpophores of Phyll. Brodiaei, 

 on which the female organs are borne (vid. 2, p. 32, Figs. 46, 47). I 

 have not been able to ascertain definitely whether our Actinococcus can 

 enter its host by means of the opening caused by the projecting 

 trichogyne. Very probably it does, as I have seen Actinococcus-be&r'mg 

 shoots of Phyllophora, in the cortical layers of which could be seen 

 what were apparently remains of undeveloped carpogones. Antheridia 

 and procarpia, moreover, do not occur on the same plant. 



In the autumn it is possible to observe the entrance of Actinococcus 

 into Phyll. Brodiaei by the small ostioles of the antheridial cavities. 

 The spores (tetraspores or carpospores) which ultimately give rise to 

 the nemathecia of Actinococcus subcutaneus germinate on the surface of 

 the host about this time. 



