210 SUMMARY OF CURRENT RESEARCHES RELATING TO 



creature is contained in the idioplasm of the fertilized egg-cell ; by tlie 

 activity of the nuclei simpler organs, such as the germinal layers, first 

 appear ; then come more developed structures, such as the enteric, nervous, 

 and osseous systems ; all these developments have one and the same mole- 

 cular structure of the nuclei, modified in various types, and slightly variable 

 in the individuals of a given type ; but this is of such a kind that the idio- 

 plasm has essentially the same structure in every stage of development. 

 But it is not to be supposed that the later organization is to be found in 

 rudiment in the idioplasm of the fertilized egg-nucleus. All that is neces- 

 sary to suppose is that typical regular movements take place in the nuclei, 

 and that these are dependent on the structure of their idioplasm. 



Let us suppose that in one case a fertilized egg-cell divides into quite 

 equal parts n times, and in other n -{- x times, we shall have two aggregates 

 of cleavage-spheres varying in size. If, then, there are more nuclear divi- 

 sions in thickness and breadth in one organism than in the other, we shall 

 have fresh difi'erences ; and thus in every rudimentary organ a new type 

 may arise by a special multiplication of nuclei in kind and number. 

 Finally, we have histogenesis which is again referable to nuclei, where the 

 idioplasm is for a long time the same in all the nuclei, but at last becomes 

 quite lost in certain elements (blood-cells of mammals, integumentary 

 scales, &c.). 



Development and Significance of the Germinal Epithelium in the 

 Testicle of the Chick.* — Prof. F. Laulanie comes to the conclusion that the 

 elements of the testicle of the chick have no genetic relation to the germinal 

 epithelium or to the Wolffian body ; these elements arise in the stroma of 

 the genital epithelium by a simultaneous difierentiation ; the germinal 

 epithelium becomes the seat of an active proliferation, which has not hitherto 

 been perceived ; the nucleus of the cylindrical cells undergoes segmenta- 

 tion, the ovules divide, and at certain points penetrate into the sub-epithelial 

 connective zone. These facts prove the tendency of the germinal epithelium 

 to develope cortical ovules at the periphery of the testicle, while the 

 seminiferous tubes are formed in its interior. Prof. Laulanie thinks that, 

 the male elements having no common origin with the female elements, 

 the double effort points to a morphological duality. This idea of the 

 hermaphroditism of the testicle is supported by the fact that the evolution 

 of the germinal epithelium is seen only in the left testicle ; one law, 

 therefore, regulates the development of this epithelium in the two sexes, 

 and affords another argument in favour of an organic and primitive 

 hermaphroditism. 



Conditions of Tadpole Metamorphosis.j — Dr. D. Barfurth gives a 

 detailed account of the series of experiments on tadpole development, as 

 the result of which the following conclusions were established : — (1) low 

 temperature retards metamorphosis, (2) quiet curtails it, (3) fasting also 

 shortens it, (4) cutting off the tail is either without influence on the meta- 

 morphosis or retards it, (5) in the majority of cases one of the anterior 

 extremities, usually the right, has the start of the other. In an appended 

 paper he emphasizes the influence of hunger, or rather fasting, as a factor 

 in development. In tadpole metamorphosis the extremities are completely 

 developed some time before they are able to break through the covering 

 skin. This liberation takes place as the skin becomes thinner and less 

 firm. This is brought about by absorption of the elements of the cutis, 

 which obviously takes place more rapidly in fasting animals, so that fasting 



* Bull. Soc. Hist. Nat. Toulouse, xx. (188G) pp. 13-6. 

 t Arch. f. Miki-. Aiiat., xxix. (1887) pp. 1-34 (1 pi.). 



