INDUSTRIAL PROGRESS DURING THE YEAR 1874. exxxiii 



of the production of sexes at will is one the solution of which 

 will "remain for a long time in a condition of illusory hope." 

 Professor E. van Beneden, of Liege, considers that the proc- 

 ess of fecundation in animals consists in the union of an ego- 

 with a certain number of spermatozoids, this act having no 

 other end than bringing together chemical elements of op- 

 posite polarity, which, after having united for a moment in 

 the egg, separate again ; for in most animals, as soon as the 

 division of the yolk into two portions appears, the elements 

 out of which the outer layer is formed are already separated 

 from those which constitute the internal layer of the embryo. 

 The new individual is formed at the moment when the union 

 between the elements of opposed polarity is effected, as ab- 

 solutely as the molecule of water is formed by the union of 

 atoms of hydrogen and oxygen. Van Beneden maintains, 

 from the facts afforded by other embryologists,that the same 

 sexual differences occur in the two embryonal layers of the 

 vertebrates as in the polyps, and he thinks it probable they 

 will be found to exist in all animals. This bears out the 

 prevalent idea that the sex of animals is determined at the 

 time of impregnation. 



M. Da rest e gives in the Archives of Experimental Zoolor/y 

 a memoir on the origin and mode of formation of double 

 monsters. 



An interesting paper on the sound produced by European 

 fishes, by M. Dufosse, appears in the Annates des Seie?ices J\ r a- 

 turelles, while M. Baudelot prints in the Archives de Zoologie 

 Experbnentale a paper on the scales of the bony fishes. 



Some interesting remarks on hybridism among ducks have 

 been made by Dr. Brewer. For a large proportion of re- 

 markable cases, where the evidences of the parentage on 

 both sides are well marked, the common mallard duck fis:- 

 ures as one of the parents. The specimens described by Au- 

 dubon as Anas Breiceri, the like of which has never since 

 been obtained, is presumed to have been a cross between the 

 wild mallard and the gad wall or gray duck. A cross be- 

 tween a male canvas-back and a female tame mallard exist- 

 ed for several generations, preserving with a remarkable de- 

 gree of uniformity the markings of their origin. The so- 

 called Cayuga Lake duck had the characteristic peculiarities 

 of the male mallard and the female Muscovy. The race of 



