i 



TRANSACTIONS OF THE SECTIONS. 77 



confessed, indeed, that the published proceedings (as distinguished from special 

 reports) of the Section of Physiology make no great show in the series of volumes 

 issued by the Association ; but, without undervaluing the reports of these pro- 

 ceedings, I would venture to say that they are not, and cannot well be, a just 

 measure of the useful work done. Much of the good eifected by the sectional 

 meetings can never be recorded. I remember being present at an assembly of the 

 German Association of Naturalists at Berlin in 1828, and of hearing Olten, one 

 of the most distinguished members and original founders of that institution, 

 declare that the great pm-pose of the Association was, not to listen to long and 

 elaborate communications, but rather to bring men of kindred pursuits from dif- 

 ferent parts into friendly relation with each other, affording them the opportunity 

 of freely exchanging information, exhibiting new and interesting specimens and 

 experiments, offering mutual suggestions, and establishing useful correspondence. 

 All, I feel sure, will admit that this promotion of friendly intercourse among men 

 engaged in the pursuit of science and those interested in its advancement is (and 

 let us hope it will long continue to be) one of the great benefits conferred by the 

 British Association. 



On the Preservation of Fishing Streams. By Sir Jajtes E. Aiexaxdek. 



Notes on the Sinicture of certain Hydroid Medusce. 

 By Professor Allma:n^, M.D., F.B.S. 



I. Slabbeeia. 



It is well known that in Slahheria there occurs upon each of the fom* radiating 

 canals a definite oval enlargement, which so closely resembles, in external appear- 

 ance and in fposition, the generative pouches of Ohelia, and of several other 

 Hydroid Medusre, that a similar function has been hitherto, without hesitation, 

 assigned to it. It has, however, nothing to do yAih generation ; it consists of a 

 mere thickening of the walls of the canal, and in no case could any trace of ova or 

 spermatozoa be detected in it. 



It is in the walls of the inanubrium that the generative elements are developed, 

 and the manubrium becomes enlarged by their presence for a definite extent, 

 exactly as in Sarsia. Nothing, however, has been discovered which seems capable 

 of throwing further light on the import of the enlargements of the radiating canals. 



It will be thus seen that Slahheria belongs to that group of Hydroid Meduss 

 which produces its generative elements in the walls of the manubrium instead of in 

 special generative buds developed from the radiating canals. In other words, it 

 belongs to the true "gonophore" rather than to that form of Medusa to which 

 the author had elsewhere given the name of " blastocheme." 



Forbes, the founder of the genus, misled by the peculiar dilatations of the 

 radiating canals, and not recognizing the presence of generative elements in the 

 manubrium, regarded Slahheria as a blastocheme; and this view has since been 

 accepted, although the presence of distinct ocelli and the absence of lithocysts 

 might have raised doubts as to its justice. 



It may be noticed that Agassiz describes dilatations of the radiating canals in a 

 North American Pmnaria, and regards them, though -with some hesitation, as 

 generative sacs. There can, however, be little doubt that the medusa of Pennaria 

 is a true phanerocodonic gonophore, having its generative elements developed in 

 the walls of its manubrium ; and it is by no means improbable that the dilatations 

 of the radiating canals in Pennaria may have the same significance as those in 

 Slahberia. 



H. On some pectdiariiies in the Structure of Obelia. 



The little medusa which forms the subject of the present notice is produced by 

 the very common hydroid Ohelia (Laomedea) yetiicidata, from whose gonangia it 

 may be seen escaping in shoals _ during the whole of the spring and summer 

 months. The marginal tentacles in the recently liberated medusa are twenty-four 

 in number. Of these four are radial, being situated in the same meridional planes 

 with the radiating canals, and 1)etween every two radial are five interradial ten- 



