166 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Yolk-organ of Salmo fario.* — Dr. Siegmund v. Schumacher points 

 out that in spite of the numerous researches on the embryology of bony 

 fish, little is known of the absorption of the yolk-sac, and he has studied 

 this process in the river trout. As is well known, in the trout the 

 communication between the gut and the yolk-sac is early obliterated. 

 At the time of hatching the yolk-sac consists of the following parts : 

 in the centre an almost homogeneous mass of yolk; round this a layer 

 containing yolk-spheres and prolongations of the protoplasmic sheath, 

 which surrounds the median layer on its outer side ; these three layers 

 constitute the yolk. Outside the yolk is an endothelial layer, which is 

 the splanchnopleure, and is separated hy a narrow coelomic cavity from 

 the somatopleure and body-wall. At the time of hatching the proto- 

 plasmic layer of yolk contains oval yolk-nuclei, constituting a yolk 

 syncytium ; at a later stage these have disappeared, and their place is 

 occupied by bodies of irregular shape, which give the staining reactions 

 of nuclei, but are not parablasts or merocyte nuclei, but are remnants of 

 degenerating vitelline vessels, and finally break down and disappear. 

 The author ascribes considerable importance to the protoplasmic layer 

 as an agent in yolk-absorption, both in the earlier and in the later 

 stages, but believes that the peritoneal epithelium of the yolk-sac is also 

 of importance in this respect. 



Development of Galeus antarcticusf — Edgar E. Waite has been 

 able to make some observations ou embryos of this fish. As was shown 

 by the late Prof. T. J. Parker, the embryos lie in separate compartments 

 of the uterus, enveloped in membranes which, though of maternal and 

 not foetal origin, foreshadow the chorion and amnion of higher forms. 

 It now appears that these membranes are produced by the shell-gland, 

 and are to be regarded as vestigial shells. The shell-gland itself is of 

 somewhat remarkable shape. In the young foetus the yolk-sac is also 

 highly peculiar, the cord being very long, and the sac itself elongated. 

 An examination of the chambers of the uterus shows that this shape is 

 determined by the space at the disposal of the foetus. 



Life-history of Clupea sprattus.J — Guido Schneider remarks that it 

 has been long maintained that the sprat does not lay eggs in the eastern 

 regions of the Baltic, but migrates westward before becoming ripe. So 

 long ago as 1894 he found ripe sprats in the Gulf of Finland, but this 

 did not prove that the eggs are capable of fertilisation and development 

 in water of such low salinity as that of this bay. Later the author found 

 pelagic Clupoid eggs which, from their size, he hesitated to ascribe to the 

 sprat. Subsequent captures have, however, shown that the developing 

 etigs in this region differ from the unfertilised and from those found in the 

 North Sea, in that they have a greatly developed perivitelline space. 

 This increases the bulk of the egg and lowers the specific gravity, so that 

 it is an adaptation to life in water of low salinity. The lame have 

 similarly a large yolk-sac, which enables them to float in water in which 

 herring larvse would sink. 



* SB. k. Akad. Wiss. Wien, cix. (1900) pp. 675-99 (1 pi.). 



t Records of Australian Museum. Sydney, iv. (1902) pp. 175-8 (1 fig.). 



J Zool. Anzeig., xxv. (1901) pp. 9-11. 



