ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 35 



the numbers of the chromosomes in the two parents. Wodsedalek 

 denies that fertility ever occurs in mules, but Goldsmith cites Lloyd- 

 Jones to the effect that female mules and " hinnies " may be the mothers 

 of colts. Goldsmith has been "unable to find any record, either 

 authentic or otherwise, of a reproducing male mule." There seems to be 

 a lack of facts in this and other discussions of the sterility of mules. 



J* A. J.. 



G-erm-plasm of Ostrich.— J. E. Dueeden {American Naturalist^ 

 1919, 51, 312-37). "Without any hesitancy it can be affirmed that 

 in the course of the fifty years during which the ostrich has been 

 domesticated, it has never produced a feather variation, germinal in its 

 origin, such as could be regarded as of the nature of a sport or 

 mutation." The germ-plasm is often very conservative. " The greatest 

 mixture of germ-plasm is going on, but no single hereditary factor or 

 determiner is altered in the process, and has not altered throughout the 

 history of ostrich breeding ; only new combinations are formed of factors, 

 already available." Crossing does not originate novelties. Artificial 

 selection does not in the case of ostriches do more than sift out the 

 possessors of certain characters and bring them together so as to effect 

 a desired combination in the progeny. The germ-plasm changes as 

 between the northern and the southern ostrich have resulted entirely 

 from internal physiological causes. In many respects the degeneration 

 phenomena in the ostrich appear to be best understood on the conception 

 of autonomous changes and variations in potency of the germ factors. 

 It is possible that by inbreeding an inherent tendency towards reduction 

 (e.g. towards the loss of toe-scales) may be accentuated. J. A. T. 



Asymmetrical Duplicity in Chick. — Noel Taylor {Proc. Zooh 

 Soc, 1919, 83-109, 3 pis., 2 figs.). Description of a blastoderm showing 

 asymmetrical duplicity, unique in the respect that both of the embryonal 

 formations exhibited gross structural defects. It seems explicable only 

 on the monozygotic theory of origin, i.e. that both centres originated 

 through some kind of disturbance from a single and possibly normal 

 germ. The primary modification induced in the larger embryonic 

 formation resulted in the inhibition of the normal growth of the 

 anterior portion of the nervous system and of the formation of the head- 

 fold. From this there followed various secondary modifications. 

 Although no true head-fold could have been present, there was never- 

 theless a well-developed fore-gut. While it has been experimentally 

 demonstrated that the material of the primitive streak does not enter 

 into the formation of the brain, it appears from the case in question 

 that the material from which the anterior region of the medullary plate 

 normally arises may under certain circumstances have the power of 

 * giving rise to a primitive streak-like mass of tissue. The importance of 

 the case is that the two embryonal formations were from the first unlike^ 

 the asymmetry being intimately bound up with the actual origin of 

 the two centres of embryonal formation from a single centre, and not 

 resulting from secondary modification in the course of development. 



J. A. T. 



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