Linncean Society. 51 



gated body, narrowed in front, divided transversely into verte- 

 bral lamella?, without dorsal cord, or sensitive organs, but fur- 

 nished with a heart, of which the contractions were sometimes 

 very lively. 



These observations, as M. Lereboullet well observes, appear 

 to prove that the generally received opinion that double monsters 

 are produced by the fusion of two embryos is perfectly correct, 

 whilst that which attributes a separate vitellus to each of these 

 embryos is not founded in fact. He considers that his observa- 

 tions, with those of Valentin, show that there is only a sing]e 

 germ, but that this, by becoming developed in two directions, 

 instead of one as in normal cases, gives rise to two more or less 

 distinct embryos. In his opinion the ridge of the blastoderm 

 (bourrelet blast odermique) plays a most important part in the 

 formation of the embryo, and in fact constitutes the " true em- 

 bryonic germ, which is always simple and single, like the vitel- 

 lus which is covered by the blastoderm, but when its develop- 

 ment is deranged from its regular course, is capable of vegetating 

 like the substance of which the bodies of polypes are composed, 

 so as to produce various forms, which however, in their subse- 

 quent development, always show a distinct tendency to return 

 to the original type of the species.^' 



PROCEEDINGS OF LEARNED SOCIETIES. 



LINN^AN SOCIETY. 



December 5, 1854. — William Yarrell, Esq., V.P., in the Chair. 



Mr. Ward, F.L.S., exhibited two sets of specimens of Asplenium 

 lanceolatum, from Jersey, both found growing on disintegrated 

 sandstone, exhibiting a striking difference between the growth of 

 the same species on an open sunny bank and in dense shade. 



Mr. John Hogg, F.R.S., F.L.S., exhibited some scales, and a 

 piece of the scaly covering which was cut from the back of a large 

 fish found in the river Tees, in September of this year. He stated 

 that two fishermen observed a great fish — such as they had never 

 before seen — left by the tide on a sand-bank, in the estuary of the 

 river Tees. They described it as having the head of a salmon, with 

 the back-fin like that of a perch, erect, and somewhat spiny, and 

 the tail spreading and much curved. The colour they did not men- 

 tion, except that of the back, which was represented as being of a 

 purplish-black. They likewise particularly observed some large 

 scales on the front of the fish near the gill-covers, one of which Mr. 

 J. Hogg also exhibited, and which is of a very strong bony texture. 

 From the account of this fish so given, Mr. Hogg conceived that it 

 could only have been a large Tunny {Thynnus vulgaris of Cuvier), 

 which had been stranded whilst in pursuit of herrings or other small 



4* 



