Observations on British Zoophytes. 441 
scribed the occurrence of certain vesicles on the branches of 
the Coryne exima, which, although possessing a strong re- 
semblance to the reproductive sacs of the zoophyte, and 
formed of all the proper tissues of the coenosarc and its 
coverings, were distinguished from those organs by each 
enclosing a single living Pycnogon, which, in the smaller 
vesicles, was embryonic, while in the larger it presented an 
advanced stage of development. A similar observation was 
made by Mr G. Hodge (Ann. and Mag, N. Hist., ser. 3, vol. 
ix.), who considered that the sacs were modified or stunted 
branches of the Coryne, the development of which had been 
arrested by the presence of the enclosed Pycnogon. On read- 
ing the papers of these gentlemen, I remembered that I had, 
some time before, been much puzzled by the discovery of 
armless Pycnogons resembling Mr Hodge's figure (pi. iv. 
fig. 10, op. cit.) in several altered polyps of a specimen of 
Hydractinia. In this case two or three were found in each 
polyp, which had assumed the form of a dilated and trans- 
parent sac crowned by its usual tentacles. The polyps ap- 
peared to be bloated and overgrown under the use of their 
Pycnogon diet. Mr Hodge's paper at once set me on the 
look-out for another specimen of Hydractinia tenanted by 
Pycnogons, and this I at last obtained by the kindness of my 
friend, Dr Wilson, Demonstrator of Anatomy at the Univer- 
sity of Edinburgh. In this, one of the polyps contained 
three larvse of a pale yellow colour, which appeared, as far 
as could be seen without injuring the polyp, to be destitute 
of legs. When first observed, the polyp was furnished with 
its proper complement of tentacles ; but as the development 
of the Pycnogons proceeded, the tentacles were absorbed, and 
the polyp became a long sac pointed at its upper extremity, 
and fitting closely on its contents, which appeared to be em- 
bedded in the longitudinal folds of the highly-developed 
endoderm. Mr Hodge supposes that the larvse, at a very 
early stage, are swallowed by ordinary alimentary polyps 
of the Coryne, and carried through the tubes of the coeno- 
sarc, until they arrive at a part which is about to become a 
polyp, which thereupon has its destination altered. And 
I think there can be little doubt that his surmise is correct, 
