442 Proceedings of the Royal Physical Society. 
as in Coryne all Pycnogon sacs, in all stages of development, 
are not only destitute of tentacles, but are, according to 
Professor Allman, covered by a layer of the chitinous poly- 
pary or scleroderin. Such a mode of nidification, however, 
could not take place in Hydractinia, the coenosarcal tubes 
of which are of exceedingly small calibre. Accordingly, we 
find that the Pycnogon sacs in this zoophyte are formed, 
not by the arrest or change in development of an immature 
polyp, but by the degeneration of a tentacled polyp previ- 
ously perfect. 
Perhaps I ought to mention here, that globular sacs are 
occasionally found in place of the polyp, in Coryne glan- 
dulosa (Daly ell). These are destitute of scleroderm, and 
lined with a very dense brown endoderm, arranged in some- 
what reticulated folds. As far as I observed, they were empty, 
and, by constantly undergoing alternate processes of dilata- 
tion and contraction, appeared to influence the circulation 
of the zoophyte, It is possible that minute Pycnogons may 
have existed in these sacs. 
VII. Report 0/ the Committee on Marine Zoology. By George Logan, 
Esq., W.S., Convener. (Specimens were exhibited.) 
The Committee had several excursions in the Firth of 
Forth during the past season, and were occupied in trawling 
and dredging, and also in sweep-net fishing on the shore. 
Upon the 11th of May last, among numerous specimens of 
Mollusca procured ofi' Inchkeith, the following only were 
worthy of notice ; recorded by Dr. M'Bean : — 1st, The 
bivalve, Cardium norvegicum of Spengler, alive ; 2d, The 
bivalve, Montacuta suhstriata of Montagu, also alive, on 
Spatangus purpureus ; 3d, The univalve, Apenhais pes 
pelicani of Linnseus, alive, — it lived until the 10th of 
September; 4th, The univalve, Pileopsis Hungaricus, or 
Fools-cap limpet, — it was also alive upon Modiola modiolus^ 
and lived until the 20th of June ; and 5th, The Echinus 
thy one papillosa, which spawned upon the 18 th of June, and 
died next day. 
Mr William S. Young recorded a specimen of the Psolus 
phantapus, which came up upon a baited line near Inch- 
