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HARDWICKE'S SCIEN CE- GO SSIP. 



nents, and are of great size. How can this be 

 accounted for ? and is there anything to explain the 

 fact? First, as regards the islands, it seems 

 geologically evident that they, comparatively re- 

 cently in geological time, formed a part of the great 

 Asio-African continent, and that when the separa- 

 tion took place, the ancestors of all these gigantic 

 and brevipennate birds were shut up in the islands, 

 together with smaller birds, with the same lax 

 plumage and feeble powers of flight, those only of 

 large size and swiftness of foot escaping from their 

 natural enemies shut up with them. That a ravenous 

 and active enemy in a small island would soon cause 

 the extinction of a small and feeble brevipennate 

 bird, is seen by what happened in theSamoan group 

 of islands. There was a Dodolet, the Did/iuculus 

 strigirostris, a pet with the natives, and a connecting 

 link between the true pigeons and the Dodo. 

 European vessels touching at these islands left 

 behind them rats, which increased and multiplied 

 until, like Dick "Whittington's so-called cat of 

 fable, but not the ship of reality, they introduced 

 the domestic cat ; it not only kept down the rats, 

 but destroyed the Didunculus, which became, as 

 was believed, extinct, until a few months ago living 

 specimens were found, and wrongly described in 

 the journals as the true Dodo. 



The Silk Fowls. — Absence of wings and hairiness 

 of plumage is seen under domestication in what are 

 known as Silk Eowls. The origin is said to have 

 been from an ordinary pair of Chinese fowls. A 

 single bird thus clothed was hatched from an egg 

 laid by the hen, the cause, though determining the 

 variation, being unknown. By a careful and long- 

 continued selection of the offspring of this fowl, 

 showing the most complete tendency to develop 

 the peculiarity of feathers, the breed of silky Cochins 

 was at length established. It is well known to 

 pigeon-fanciers that similar laxity of plumage exists 

 among them. Given, therefore, a tendency to laxity 

 of plumage, aud but moderate powers of flight, 

 natural selection will explain, on Darwin's hypo- 

 thesis, how, as the powers of flight diminished, only 

 the larger and more powerful would survive, while 

 the smaller and feebler would easily fall a prey to 

 their natural enemies, while the use of the legs and 

 disuse of the wings would also in time produce the 

 swift and strong cursores like the Ostrich, Emeu, &c. 



A New Carex.— Messrs. "Whitehead and Newton 

 write to us concerning a new carex [Carex ornitlto- 

 poda), which they first detected in Miller's Dale, 

 Derbyshire, in 1874. They gathered it again on the 

 dry and exposed parts of the limestone rocks in the 

 same neighbourhood this year, and now offer in our 

 exchange columns. It is a very interesting dis- 



. ON THE DEVELOPMENT OF HYDRA 

 VULGARIS. 



By James Ftjllagar. 



[Our readers are well aware that this careful observer has 

 already contributed several important articles on the above 

 subject to our Journal. We have now the pleasure of insert- 

 ing' one from the "Journal of the Quekett Microscopical 

 Club," in continuation of the same series of investigations. 

 — Ed. S.-G.] 



IT appears from the statements of various writers 

 on Natural History, that the development of Hydra 

 from ova has never or very rarely been witnessed, 

 though, at the same time, no doubt is entertained 

 of the fact that one of the means of its reproduction 

 is fro.ri ova. I have had //. vulgaris and H. viridis* 

 under my observation for more than three years 







Fig. 100. Ouim of Hydra vulgaris, a, transparent envelope; 

 b, short spines; c, triangular- shaped markings on envelope. 



past, and, after various failures and disappointments, 

 I have at length succeeded in witnessing the 

 hatching out of several specimens of Hydra vulgaris. 



Fig. 101. 



D, appearance of envelope before the rupture of 

 the egg indicated at E. 



covery. 



Hydra vulgaris differs in many respects from 

 Hydra viridis. The egg is larger,! and studded 

 with what appear to be short spines (fig., 100, b). 



* A paper on the Development of Hydra viridis from_Ova 

 will be found in Scienck-Gossip for 1873, pp. 12 and ITS. 



