2 NOTES AND COMMENTS [jaxuaky 



In two or three months they are regenerated, alike as regards bony and 

 horny tissue. The regeneration of the mandibular portion proceeds 

 more slowly than that of the upper parts. The author entitles his 

 paper " Cas de regeneration clu bee des oiseaux explique par la loi de 

 Lessona" (C. B. Soc. Biol., July 1898), but as Lessona's law is hardly 

 as familiar as Boyle's we may be allowed to state it. In 1868, the 

 illustrious Italian naturalist formulated the conclusion that in animals 

 the parts which are capable of regeneration are those which run most 

 risk of mutilation. This conclusion has been restated by Darwin and 

 by Weismann (whose name the author spells in the usual French 

 fashion) in the thesis that regeneration is an adaptive phenomenon. 

 Weismann found some difficulty in regard to a stork which repaired 

 the terminal half of its mandibles. But Bordage points out that male 

 storks fight furiously. After this who can deny that cock-fighting 

 has its utility ? 



A Delicate Operation. 



In a short paper entitled "Embryons sans noyau maternel" (C. R. 

 Ac. Sci. exxvii. (1898), pp. 528-531) Professor Yves Delage describes 

 a remarkable experiment. He divided the egg of a sea-urchin under 

 the microscope into two parts, one containing the nucleus and the 

 centrosome, the other simply cytoplasmic. Beside them he placed an 

 intact ovum, and then let spermatozoa in. All the three objects 

 showed equal " sexual attraction," all were fertilised, and all 

 segmented, the intact ovum most rapidly, the nucleated fragment 

 more slowly, the non- nucleated fragment more slowly still. 

 In one case, the development proceeded for three days ; the 

 intact ovum had become a typical gastrula, the nucleated fragment a 

 smaller gastrula, and the non-nucleated fragment also a gastrula, but 

 with very much reduced cavities, " presque virtuelles." All the cells 

 showed nuclei. The experimenter concludes that fertilisation and some 

 measure of development may occur in a fragment of ovum without 

 nucleus or ovocentre. It is probably by these indirect paths that we 

 shall eventually discover the real nature of fertilisation. According to 

 Delage, two things must be distinguished — («) the stimulus given to the 

 ovum by a specially energetic kinoplasm brought in by the sper- 

 matozoon, perhaps in its centrosome ; and (b) the mingling of heritable 

 characteristics, or amphimixis. It must, of course, be observed that 

 while the fertilised cytoplasmic fragment in Delage's clever experiment 

 segmented, it did not really develop. 



Birds and their Surroundings. 



The British Museum (Natural History) has recently placed on ex- 

 hibition a model by the American ornithologist, Mr. A. H. Thayer, 



