46 SUMMARY OF CURRENT RESEARCHES RELATING TO 



three to twenty minutes, according to its age, and ova do not develope. 

 In 1 per cent, solution of marine salts a tadpole dies at the end of 

 some hours, unless it has been previously prepared by a series of 

 solutions of 2, 4, 6, 8 per 1000. Experiments were made with young, 

 placed some in fresh water and others in solutions of 2, 4, 6, 8 per 

 1000, and it was seen that the tadpoles developed the more slowly the 

 more concentrated the solution. When the water was kept undulating, 

 tadpoles developed even when the solution contained 12 parts per 

 1000 of marine salts. 



Influence of the Number of Individuals in One Vase, and of 

 the Form of the Vase on the development of Tadpoles.* — M. E. 



Yung concludes from his experiments that the time taken in the 

 development of tadpoles is proportionately as long as their number is 

 greater in the same quantity of water, when there is an ample supply 

 of food. This influence of the water supply has already been demon- 

 strated by Prof. Semper to be true of Lymnseus, but M. Yung does 

 not accept the explanation that there is some as yet unknown matter 

 in the water which is the cause of this ; it rather appears to him to 

 be a question of aeration. For he found that the tadpoles develope 

 the more rapidly the greater the diameter of the vessel which contains 

 them, and consequently, the greater the surface of aeration. How far 

 pressure has anything to do with the matter must be reserved for 

 further experiments. 



Relations of Yolk to Gastrula in Teleosteans.f — Mr. J. T. 

 Ounningham describes the ova of Gadus seglifinus, G. morrJiua, 

 G. merlangus, and Trigla gurnardus. He was able to observe in the 

 eggs of cod and haddock that the cells of the blastoderm are, at an 

 early stage, continuous with those of the periblast ; but the invaginated 

 layer of the germinal ring is not so continuous ; the whole edge of 

 the blastoderm represents the ancestral blastopore, and the formation 

 of the embryo by concrescence is merely the closing of the blastopore 

 from before backwards. The edge of the blastoderm in Amphibia, 

 Petromyzon, and Ganoids is homologous with that of Teleostei. But 

 the edge of the Elasmobranch blastoderm is not so homologous, the 

 inflected part representing the whole of the Teleostean edge. The 

 anterior part of the primitive streak in Sauropsida is regarded as 

 representing the ancestral blastopore, while the posterior part re- 

 presents the coalesced uninflated part of the blastodermic rim in 

 Elasmobranchs ; the edge of the Sauroid blastoderm seems to corre- 

 spond to a hernia in the blastoderm of Elasmobranchs. Part of the 

 periblast probably forms the floor of the intestine, and the rest forms 

 part of the splanchnopleural mesoblast. 



Ova of Callionymus lyra.| — Prof. W. C. M'Intosh finds that the 

 ova of this fish are pellucid and pelagic ; they are very small, and are 

 invested, when mature, in a very fine hyaline zona radiata ; they may 

 be distinguished by their external hexagonal reticulations. 



* Comptcs Rendns, d. (1885) pp. 1018-20. 



t Quart. Journ. Mif^r. Sci., xxvi. (1885) pp. 1-38 (4 pis.). 



J Ann. and Mag. Nat. Hi.st., xvi. (1885) pp. 480-2. 



