174 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Conditions of Development in the Frog.* — Dr. 0. Schultze has re- 

 investigated tLe questien whether the power of rotation is an essential 

 condition of development of the egg, or whether normal development 

 may recur in an egg kept in a pesition of constraint. Two n ethods off 

 experiment are available: — (1) that of Pfliiger, consisting in lemoving. 

 the eggs from the ovary, fertilising them in a mere drop of water con- 

 taining speimatozoa, so that the albuminous investment swells but little,. 

 and then allowing them to develope in a moist chamber; (2) that adopted 

 by Eoux and others, consisting in placing the egg between two glass 

 slides, with sufficient pressure to prevent free movement of the egg 

 within its membianes. Eoth methods gave the same results, and these 

 may be summarised as follows : — r l he egg speedily dies if it is so placed 

 that it cannot respond to gravity during the process of development by 

 movements of lotation produced by the structural changes within iL 

 The phenomenon of l espouse to gravity is quite similar to the geotre pisms 

 of plants, and may conveniently receive the same name. Secondly, eggs 

 which are kept permanently fixed with the animal j)ole downwards may 

 reach the end of gastrulation, but never display a medullary groove- 

 This shows tl at the medullary canal does not develope in the colourless 

 hemisphere (f the egg, hut above the dorsal lip of the blastopore, and 

 the dorsal lip of the blastopore does not unelergo displacement towards. 

 the upper surface of the egg, as has been supposed by Koux. 



Physiology of Reproductive Elements.! — £>r. J- F. Gemmill las- 

 made a series of experiments en various points connected with the 

 phjsiology of ova and speimatezoa, in organisms, such as sea-urchins and! 

 the limpet, where there is no jailing, and no means of ensuring fertili- 

 sation. First, as to vitality, sea-urchin eggs were tested as to capacity 

 for nomal development, after fertilisation at different periods after 

 sledding. It was found in the first place that the vitality of the ova 

 depends on the state of the urchin, being greatest when the urchin is 

 perfectly ripe, least when it is enly partially mature or nearly spent- 

 Further, the best results were obtained when the eggs were fertilised 

 about 1-4 hours after shedding, polyspermy and irregular development 

 being con moner in eggs which were fertilised immediately after shedding; 

 than in those which were allowed to lie in sea-water for this period. 

 Up to the ninth hour after extrusion the egg6 show little loss of vitality., 

 but after this a gradually decreasing number develope normally, until 

 at the end of 28 hours all appeared eh ad. The life of the free 

 egg is thus markedly limited. Much the same results were obtained 

 with limpets, except that the life of the egg is somewhat longer. As 

 regards the vitality of the speimatezoa, it was found that this varied 

 with the number present in the sea-water. The speims are nourished 

 by the speimatic fluid ; and if this be greatly diluted, death cccuis more 

 lapidly than it otherwise would. The most advantageous proportion is 

 that of 1 part of spermatic fluid to 10 of sea-water, and in this the 

 speims will live about 72 hours. In the case of limpet sperms, the 

 duration of vitality is slightly longer. 



A number of experiments were made as to the limit of travel of 

 g permatczoa in still water. In open vessels this limit was found to be 



* Arch. Mikr. Anat, lv. (1899) pp. 202-30 (1 pi. and G figs.), 

 t Journ. Anat. Physiol., xxxiv. O90U) j.p. 1G3-81 (0 figs.). 



