STRETHILL WRIGHT, ON BRITISH ZOOPHYTES. 51 
am convinced that no other zoophyte occurred on the shell, 
or in the water in which it was placed. 
Medusoid of Trichydra pudica ?—Umbrella ritre-shaped, 
covered with minute thread-cells. Swb-umbrella with four 
lateral canals, destitute of ovaries or sperm-sacs. Peduncle 
short, cylindrical, four cleft at the mouth. Tentacles four, 
short, with two or four intervening tubercles. Oolites 
absent. Hye-specks absent. 
9. On the Development of Pycnogon-Larve within the Polyps 
of Hydractinia echinata. Communicated to the Roy. 
Phys. Soc., May 7th, 1862. 
In a communication made by Professor Allman to the 
British Association in 1859, entitled, ‘On a remarkable 
form of Parasitism among the Pycnogonide, the author de- 
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 ccenosare 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 Pyenogon. 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 (pl. 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 
Pyecnogon 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 larve 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 Pyenogons proceeded, the tentacles were absorbed, and 
the polyp became a long sac, pointed at its upper extremity, 
