1903.] On the Nematocysts of Solids. 465 



1 . An E. alba, found on a colony of Paripha, had nematocysts of two 



kinds, indistinguishable from those of the hydroid. 



2. An E.rufibranchialis, found on Eudendrium, had nematocysts about 



one-third the size of those of E. alba. These were apparently 

 not compared with those of Eudendrium ; at any rate the result 

 of the comparison is not given. 



3. A young E. alba was found in a large vessel of sea water in 



which various marine larvae were being reared. This ^Eolis 

 must have been over 2 months without hydroid food and had 

 probably metamorphosed in the vessel. It had no nemato- 

 cysts. 



Having discussed one or two difficulties, the writer concludes that 

 further investigation of this point is desirable, and that it may turn 

 out that nematocysts are not " part of the organic make-up " of the 

 JEolidse. He is apparently unaware of Strethill Wright's work. 



II. The Nematocysts of Solids are derived from their Cwlenterate Prey. 



Before describing my experiments, which, I think, afford conclusive 

 confirmation of Strethill Wright's view, I shall proceed to discuss a 

 number of facts which have come under my own observation, or which 

 I have collected from the literature of the group, which point in the 

 same direction and would, indeed, be sufficient by themselves to prove 

 the truth of this view. 



1. Great Similarly of the Nematocysts of ^Eolidse and Coelenterates : 



I think that those who quote the nematocysts of Nudibranchs and 

 Coslenterates as a striking example of homoplasy or convergence, can 

 scarcely be aware of the astonishing completeness of this assumed 

 convergence. It is not simply a case of nematocysts of the same 

 general plan occurring in the two groups, but of each of several 

 distinct forms of nematocysts being found in both groups. For 

 instance, the most characteristic Actinian nematocysts have elongated 

 semi-cylindrical capsules; the}' are either straight, varying from 

 20 60 ju. in length, with the basal portion of the thread (twice the 

 length of the capsule) thick, and closely covered with long fine bristles 

 (fig. 7) ; or the capsule is slightly curved, about 25 p in length, and 

 narrower in proportion than in the last form, while the thread is 

 uniformly tapering, slightly spiral, and furnished with short relatively 

 stout barbs for a distance rather less than the length of the capsule 

 (fig. 8). Both these forms are of frequent occurrence in Solids 

 belonging to Bergh's sub-family Aeolidiadce proprice. 



Small nematocysts, 8 ju, or less in length, shaped something like an 

 apple pip (fig. 1), are very widespread in the hydroidea j they occur, 



