ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 537 



contact with its outer surface, and also in their becoming attached to 

 the living egg. 



The vast number of eggs, and the still vaster number of spermatozoa 

 produced, together with the motility of the latter and the action of saa- 

 currents, quite suffices to bring the male sexual cells into contact with 

 the zona pellucida. 



Many writers have supposed that chemotaxis is a constant factor in 

 the fertilisation of animal eggs. This generalisation, which has been 

 made by arguing from the attraction of the spermatozoa to the eggs of 

 certain plants, is as yet entirely without experimental justification. The 

 author's results in regard to Echinoids, which are in accordance with 

 those obtained by Mus-iart in the case of the frog, and with the work of 

 Dewitz on the fertilisation of the eggs of certain insects, lead him to 

 suppose that chemotaxis, at least for a great number of animal species, 

 plays no role wh itever in bringing the sexual elements together. 



Dispensability of Gravity in Development of Toad's Egg 1 . * — 

 T. H. Morgan has subjected the toad's eggs to rotation in water from 

 the moment of their removal from the animal, and before fertilisation. 



The cleavage of the rotating eggs progressed normally, as was de- 

 termined by removing a few of the eggs at intervals. Those removed 

 at the 2-cell stage (after 5 hours) and kept outside developed normally. 

 Eggs removed after 25 and 36 hours also produced normal embryos. 

 After 48 hours the eggs that were still rotating also showed the dorsal 

 lip of the blastopore. The eggs were kept rotating for se/eral days 

 longer, and produced normal embryo?. 



The results show that gravity need not be a determining factor in 

 the development of a bilateral plane in the apparently radially sym- 

 metrical egg. 



The critical points that now remain to be determined are:— (1) does 

 the point of entrance of the spermatozoon determine the bilaterality of 

 the egg ? (2) does the grey crescent; develop in a pre-organised part of 

 the egg, and if so, does the egg rotate after fertilisation so that this 

 part turns uppermost ? or (3) does the grey crescent appear at any point 

 on the egg that happens to lie uppermost ? But the results of the ex- 

 periments on the toad's eggs show conclusively that when gravity is 

 excluded as a factor acting in a constant relation to the egg, a bilateral 

 plane still appears in the egg. 



Early Stages in Oogenesis and the Synaptic Phases.f — A. Giardina 

 has studied these in Di/fiscus, Mantis, Helix, &c. During the growth of 

 the oocytes there is a twice repeated characteristic stage of repose, with 

 a reticular nucleus, and between these a synaptic phase is interposed. 

 But it seems necessary to distinguish the synapsis of growth from a 

 synapsis of differentiation, which also occurs in the course of oogenesis. 



Experimental Parthenogenesis in Amphibian s.J — E. Bataillon 

 finds that the unfertilised ova of Rana fusca and B. esculenta are made 

 active by heat as well as by plasmolytic solutions, an 1 that the two 

 stimuli may be advantageously combined. In these conditions the eggs 



* Auat. Anzeig., xxi. (1902) pp. 313-6. 



t Tom. cit., pp. 293-308 (21 tigs.). 



% Comptes Renrlus, cxxxiv. (1902) pp. 01S-20. 



