1865.] Zoology and Animal Physiology, <6c. 701 



birds, and on the length of time birds are capable of retaining life 

 under water, which varies much in different species, — being in the 

 duck as much as ten minutes. 



We read in the ' Comptes Eendus ' an account of the reproduction 

 of some Mexican Axolotls in the Jardin des Plantes, as observed by 

 M. Auguste Dumeril. This being the first time that such an event 

 has taken place under scientific eyes, is a matter of great interest. 

 The ovum is at first similar in appearance to those of other batrachian 

 reptiles, and consists of a black vitelline sphere contained in the 

 centre of a clear vitelline membrane, which is itself contained within 

 an albiuninous envelope. The young embryo, in about twenty-eight 

 or thirty days after spawning, becomes separated from the shell, by the 

 aid of violent movements, and then measures 0*015 of a millimetre, 

 and possesses branchiae which are much less elaborate in their divisions 

 and ramifications than they become in the adult form. A second 

 stage of development may be reckoned, embracing the period when 

 the posterior pair of limbs appears, but M. Dumeril has not yet 

 precisely made out how long elapses between this period and the 

 rupture of the egg. The anterior pair makes its appearance in the 

 earliest stage, but some months pass before the posterior limbs are 

 developed. 



M. Poluta, in the ' Annales des Sciences,' gives the results of 

 some researches upon the duration of the life of fishes out of the 

 water, which varies greatly, so that while the sturgeon will exist 

 several hours deprived of its natural element, it is well known that 

 the herring dies in about a minute. This circumstance is not de- 

 pendent upon a different structure of the respiratory organs, but 

 upon the tenacity of life in the animal fibre, which is in inverse 

 relation to the quantity of oxygen necessary to the support of life in 

 the organism. The herring requires more oxygen for the same weight 

 of body than the sturgeon ; and the circumstances which appear to 

 prolong the life of fishes out of the water appear to be these, viz. the 

 cylindrical form of the body, the presence of water in the branchial 

 chambers, and the absence of scales from the skin ; while the lateral 

 compression of the body, the aggregation of the leaves of the branchiae 

 in a mass, and the existence of scales have a contrary effect : for 

 fishes with cylindrical bodies, when removed from the water, rest 

 tranquilly upon the ground, and their branchiae have free play, while 

 the laterally compressed fishes lie upon the side, and cannot distend 

 the branchiae of the lower side. With regard to the scales, those 

 fishes which have them most deeply implanted in the skin live 

 longest, while those in which they readily separate, as the herring, 

 are very short lived ; and the same circumstances may be observed in 

 the case of lizards, tortoises, &c, whose tenacity of life is very great, 

 and in inverse relation with the quantity of oxygen necessary to sustain 

 life, while it is in direct relation to the depth of implantation of their 

 scales. 



The operculum of univalve shells has given rise to different 

 opinions as to its homologies, some supposing it to answer to the 

 second valve of bivalves, and the opercular mantle as correspondent 



3b2 



