ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 17 



degenerating cells are consumed by leucocytes. Thus degeneration 

 precedes phagocytosis, and induces it. 



Development and Structure of the Lens.* — Prof. C. Eabl con- 

 cludes his important memoir on the development and structure of the 

 lens in Vertebrata. We cannot attempt a summary of the detailed 

 results, but we would direct attention to a few conclusions of general 

 interest. Eabl discusses the recapitulation doctrine, and fiiids, in the 

 development of the lens, as elsewhere, evidence that the development 

 of an organ in a higher Vertebrate is in its early stages approximately 

 parallel to the development in ancestral forms ; gradually, however, the 

 approximately parallel lines diverge. That there is a more detailed 

 recapitulation of the characteristics of near ancestry he admits ; but 

 his chief emphasis is on the fact that the embryo is from first to last 

 a specific unity. Early stages of Vertebrate embryos can never be 

 thought of as interchangeable ; the human embryo is specifically 

 human from the ovum onwards. Similarly, from the very outset, the 

 primordium of the lens is specifically peculiar; the number of the cells 

 stands in a definite proportion to the number of the first-formed radial 

 lamellae. 



As to structure, the most important new point is Babl's emphasis 

 not on the concentric layering but on the radial lamellae. Four main 

 types are distinguished : — (a) of fishes and amphibians in water ; (b) of 

 amphibians (after metamorphosis at least), of mammals, and of some 

 snakes (JEryx) ; (c) of reptiles except snakes, and of birds ; (d) of 

 adders and vipers. But every species has its specific lens, — the organism 

 is a unity through and through. " In der Linse spiegelt sich eben die 

 ganze Lebensweise eines Thieres." 



Early Development of Mammals. — Prof. Eauber f briefly criticises 

 Edouard van Beneden's + observations on the development of the bat, 

 and claims priority for the discovery of the existence and subsequent 

 disappearance of the cell-layer called by him Deckschicht ; a claim 

 which was contested by van Beneden in his recent paper. Eauber 

 further maintains that as van Beneden regarded the Deckschicht, or 

 outer ectoblastic layer, as constituting the whole of the ectoblast, the 

 discrepancies between his own and van Beneden's observations were 

 then much greater than would appear from van Beneden's statements 

 now. 



In his reply van Beneden § points out that his discovery of the 

 Deckschicht was practically simultaneous with that of Eauber, and 

 that he has long since given up his early (1875) views as to the morpho- 

 logical value of this layer. He believes, however, that Eauber and 

 some other embryologists are equally in error in attempting to apply 

 to the layers of the didermic Mammalian embryo the terms hypoblast 

 and epiblast ; for these layers, as seen in AmpJiioxus, are certainly not 

 homologous with the layers in the bat or rabbit. 



• Zeitschr. f. wiss. Zool., lsvii. (1899) pp. 1-138 (4 pis. and 46 figs.). 



t Anat. Anzeig., xvi. (1899) pp. 523-4. 



X Loc. cit. 



§ Tom. cit., pp. 524-G. 



Feb. 21st, 1900 C 



