pm^asitic within recent Madreporaria. 



253 



coral Aclilya is the aquatic form of some aerial " fungus " which, like it, 

 devours and increases upon organic matter. 



Some of the most perfectly developed Aclilyce parasitic within corals 

 were obtained from specimens of Balanoplujllia verrucaria which came 

 from the Mediterranean, and which I kept for many months in an 

 aquarium. The vegetation in the aquarium consisted of species of Cla- 

 dophora and Bryopsis, and they grew not only on the rockwork, but also 

 on the bases and sides of the corals which had been left uncovered during 

 growth by the orange-coloured ectoderm. As some of the corals became 

 weak, their colours becoming pale, the organic or living tissue being 

 thinner and the tentacles less expanded, the weed encroached and, finally, 

 in one or two instances appeared on the septa, the living ectoderm having 

 become abraded or dead on those spots. 



After a while a bulky "mould" spread over the whole calice of the 

 coral, and decomposition soon set in. This mould consisted of extremely 

 crowded filaments with occasional dissepiments, and resembled a Botrytis. 

 It lived in the water, and grew with great rapidity. 



This fact renders Berkeley's statement that Aclilya may be an aquatic 

 form of Botrytis very probable ; and certainly the filaments of many of 

 the internal parasites of the corals greatly resemble those of Peronospora. 

 If, then, the coral-parasite follows the life-cycle of its congeners, it may 

 live under different conditions in various organisms, and receive as many 

 generic titles and specific names. 



Doubtless there is a motile stage as a freely swdmming zoospore in one 

 of the life-cycles ; and in this this feeder on organic matter relates to its 

 remote ancestry amongst the Amoeboids. 



If the arbitrary nature of all the classifications of organisms which 

 assume different shapes and habits under different external conditions be 

 admitted, the position I have assigned to the parasite as Aclilya penetrans 

 appears to be correct. But it may be more philosophical to state that it 

 belongs to a group of interchangeable forms, and that it is the marine and 

 parasitic expression of the arbitrarily separated genera Aclilya, Sapro- 

 legnia, Botrytis, Peronospora, and probably Bryopsis. 



IX. On the Occurrence of Achlya (Saprolegnia) ferax, Ktz., in 

 Caryophyllia Smithi. 



On submitting an old specimen of the common broad-based Caryophyllia 

 Smithi, from the Devonshire coast, to the action of dilute hydrochloric 

 acid, a vast amount of internal parasitic growth was obtained. This 

 growth in some respects resembles that of Achlya penetrans ; but in 

 its close reticulations of long and rarely branching filaments, of -g-^^ to 

 0,0 inch in diameter, it assimilates to the well-known parasites of 

 Anornia and Ostrea. 



The resemblance of the fructification to the drawings in Kiitzing's 



VOL. XXV. T 



