201 



Mr. Sclater exhibited specimens of two rare species of Arctic birds 

 from the collection of John Barrow, Esq., of Hanover Terrace, 

 Regent's Park. One of these was the new species of Diver with a 

 white bill, described by Mr. G. R. Gray as Colymhus adamsi *, 

 which had been also obtained in .Qapt. Collinson's expedition, on the 

 N.W. Coast of America. The other was an example of the ex- 

 ceedingly scarce Wader with a spatnlated bill, Eurinorhynchus pyg- 

 mceus (Linn.) (Gray & Mitch. Gen. of B. pi. 152), in what was ap- 

 parently its summer dress, the head, neck, and breast being rufous. 

 This was believed to be the only specimen known in this state of 

 plumage, the bird having hitherto occurred as a straggler in Asia 

 and Europe in its winter dress. The locality of this specimen was 

 supposed to be the North-eastern Coast of Asia. 



May 24, 1859. 

 G. R. Waterhouse, Esq., V.P., in the Chair. 

 The following papers were read : — 



1. On the Development of Aurelia aurita in the Society's 

 Aquaria. By E. W. H. Holdsworth, F.L.S. 



Few persons can have paid any attention to marine aquaria with- 

 out noticing in them the frequent occurrence of the little white 

 polype, commonly known as Hydra tuba. The ova producing them 

 are doubtless introduced with the sea-water ; and if the conditions 

 are suitable for their development, the rock-work and sides of the 

 tank are often studded with hundreds of their delicate transparent 

 bells. The changes they undergo before assuming the adult form 

 have been investigated by Sars, Siebold, and many other naturalists ; 

 and it is now well known that these little polypoid forms are only 

 early states of Aurelia aurita — the medusa seen thronging our coasts 

 in such countless thousands during the summer months. The per- 

 fect animal, however, is so rarely produced within the limits of an 

 aquarium, that a recent case of its occurrence in one of the Society's 

 tanks appears to me worthy of record. Since the establishment of 

 the Fish-house in the Zoological Gardens, not a year has passed 

 without the abundant production of the polypes in several of the 

 tanks, and their transverse splitting and change to medusoids have 

 been frequently observed ; but no further development has taken 

 place, and after a short period the young animals have gradually 

 disappeared. In the present year, however, greater success has been 

 attained ; and this is perhaps partly due to the water in the tank 

 having been kept at a nearly uniform temperature, from the absence 

 of any severe cold during the early part of the season. The polypes 



* Seep. 167. 



