866 SUMMARY OF CURRENT RESEARCHES RELATING TO 



developing ovum, occasioning its differentiation. The formal develop- 

 ment of the impregnated ovum is a process of complete self-differentia- 

 tion." Bern's inquiry had a different character, and dealt with the 

 morphological side of the problem. Pflliger had found that ova of 

 Mana esculenta, if placed with the white tract superior, did not 

 divide. Born, on the other hand, found that in the ova (of Mana 

 fused) with the white tract superior, that tract did not retain its 

 initial position, but either entirely or in great part dipped downwards 

 to a sub-equatorial level when cleavage commenced. In such cases 

 cleavage commenced on whatever happened to be the uppermost side 

 of the ovum, though not without exception. Born concludes that the 

 question is one of indirect influence of the force of gravity acting by 

 virtue of the characteristic arrangement and disposition of constituent 

 parts of the ovum with their varying specific weights. 



Aspects of the Body in Vertebrates and Arthropods.* — The essay 

 of A. S. Packard is a result of Sir Kichard Owen's recent study on 

 the " Aspects of the Body in Vertebrates and Invertebrates " ; its 

 special object is to present facts against the presumed homology be- 

 tween Arthropods and Vertebrates. It is pointed out that histological 

 differences are to be detected in the presence of the dotted (" mye- 

 loid ") substance in Arthropod brains, and its absence from those 

 of the Vertebrata. As to " histological topography," the ganglion- 

 cells are internal in the Vertebrate, cortical in the Arthropod ; in the 

 latter the ganglia are at first wholly formed of spherical cells, while 

 the differentiation into round central cells and cortical white substance 

 is much more early effected in the former. Indeed, in no way does 

 embryology support the doctrine of the homology of the nervous 

 system of these two groups ; and the embryos themselves are in 

 opposite positions. The characters of the investments are altogether 

 different. 



The author regards the original dispute between Cuvier and 

 St. Hilaire as being in part metaphysical, and he looks upon questions 

 of this kind as savouring more of scholasticism than of science. 



B. INVERTEBRATA. 



Function of Chlorophyll in Animals.f— L. von Graff, dissatisfied 

 with the conclusions of Brandt as to the symbiotic relations of what 

 the latter regards as green algse to Hydra viridis, and with the 

 methods of his experiments, arranged three specimens of M. viridis in 

 eight different vessels ; four of them, A, B, E, and F, he exposed to 

 the light ; A, B, C, and D were filled with water from an aquarium. 

 In E-G the water was filtered. In A, 0, E, and G the water was 

 changed daily, in the others it was never changed at all. The first 

 Hydra to die was one in glass G, on the 31st day of exposure, in 

 which the filtered water was changed daily, and the, light shut off. 

 The glass A did not lose a specimen till the 109th day of observation, 



* Amer. Natural., xviii. (1884) pp. 855-61, and Ann. and Mag. Nat. Hist., 

 xiv. (1884) pp. 243-9. 



t Zool. Anzeig., vii. (1884) pp. 520-7. 



