252 



Prof. P. M. Duncan on Thallophytes 



Saiv'olegnicB ; but a specific identity with S. ferax^ Ktz., is wanting. As 

 in another work I have absorbed Saprolegnia in Achli/a*, I propose to 

 classif y this parasite in that genus, and to name it Aclilya penetrans. 



But in thus provisionally classifying these parasites, their resemblance 

 to the filamentous rootlets of Godium and to very delicate specimens of 

 Bryopsis must not be forgotten. The large confer void-looking filaments 

 found within the interlaminar structure of the septa closely resemble 

 those of the Bryopses which cling in a close reticulation to the outside of 

 many corals, i^r^o^jsis-filaments do penetrate projecting parts of the 

 coral. The tint of the clear cytioplasm of the parasite is often pale sap- 

 green ; but there is no other evidence of the existence of chlorophyl in the 

 contents of any of its ver}^ variously shaped filaments. The Bryopsis is, 

 of course, crowded mth green granules, and doubtless chlorophyl is 

 present. The reticulate rootlets of Codium are often colourless, the 

 larger and upright portions of the plant being green. The probability of 

 the presence of chlorophyl being determined by the action of light upon 

 colourless or dark brown cytioplasm should therefore be considered 

 before an arbitrary line is drawn between the AcMyce and such very 

 remarkable forms as those included in the genera mentioned above. 



Prom the results of my examination of Upper-Silurian corals and of 

 Lower-Silurian arenaceous Foraminifera, it is evident that a parasite 

 closely resembling Achlya penetrans lived mthin them duriug those 

 remote ages. Corresponding in shape with the Silurian form of parasite 

 are others which are fossil within the corals of later ages. The main 

 differences between the ancient and the modern forms consist in the 

 larger calibre of some of the filaments of the first, their long, often 

 unbranching course, and the frequent development of Conidia-lookmg 

 bodies within them, and the spherical shape of the spores : but it is quite 

 possible that these are not distinctions which are of a specific value. 



The modern coral-parasite is evidently the descendant, with slight or, 

 possibly, no modification, of those which flourished during successive world- 

 mde changes in floras and external conditions. Hence it would, in all 

 probability, have had its life -cycle made complicated, and a metamorphosis 

 involving vegetative and mobile stages has been superadded. It is not 

 an assimilator of putrescent or rotten animal matter, but of the nitro- 

 genous and undecomposed organic basis of the coral; and in this it 

 resembles the organisms which destroy some Kving Diptera and other 

 aerial insecta. Moreover this resemblance in function is possibly caused 

 by continuance of individuality ; and if this be true, it adds vastly to the 

 difficulty of placing the parasite in a philosophical scheme of classification. 

 Empusina (the fl3^-killer) certainly is an aerial fonn of AcJdya; and 

 Empusina muscce turns into Acldya prolifera. It is, then, quite within 

 the range of possibiht}^, and, indeed, it is extremely probable, that the 



^ Micrographic Dictionarj', 1875, 8rd edit., Articles Achlya and Sap'olegnia. 

 See also Sporendo7iema and Eminisina, and Article on Confervoidete. 



