222 Mi see lla n eons . 



comprised between - 2° and + 10° C. ( = 28°-4 and 50° F.) j the latter, 

 observed in July, is probably about the maximum. In the middle 

 of the fjord, at a depth of 350 metres and a temperature of 37°'4 F., 

 upon very fine clayey mud, such forms as Ptcten groenlandicus and 

 Siphonodentallum vitreum were met with. 



The Varangerfjord and the neighbouring regions of the glacial 

 sea do not freeze in winter. Whether this is to be explained by the 

 very problematical extension of the Gulf-stream, or by the influence 

 of the great south-east to north-west atmospheric current, the exis- 

 tence of which is now proved, the fact exists that while the condi- 

 tion of its superficial waters seems to unite the Varangerfjord with 

 the Atlantic, the temperature of its bottom -waters, as also its mol- 

 luscan fauna, approximate it to those seas which are covered with 

 ice during the greater part of the year. — Ooniptes Rendus, Decem- 

 ber 11, 1882, p. 1231. 



Contributions to the Developmental History of the Prosobranchiata. 



By Dr. Cakl Habl. 



This memoir divides into two parts — the first treating of the 

 question of the ultimate fate of the gastrula-mouth in Paludina 

 vivipara, while the second relates to some later developmental 

 processes in Bythinia tentaculata. 



The question of the fate of the gastrula-mouth is of great theo- 

 retical importance ; and there is at present scarcely a point indeve- 

 lopmental history about which there has been more dispute, and 

 upon which opinions are more divided. The author finds that in 

 Paludina vivipara the gastrula-mouth gradually but completely 

 closes in the median line of the ventral surface; that, further, soon 

 after its closure the anus makes its appearance, but is in no way 

 connected with the gastrula-mouth ; and that, lastly, the permanent 

 mouth appears at the spot where the last residue of the gastrula- 

 mouth had closed up. These statements are certainly in contradic- 

 tion to those of some other authors, but show that a common 

 mode of development may be set up, at least for the Gasteropoda. 



The second part treats of the structure of the velum, the origin 

 of the upper oesophageal ganglion, the structure of the primitive 

 kidneys and the intestine, and of the development of the persistent 

 kidneys. The author finds that the velum in Bythinia is composed 

 of large cells containing vacuoles, and differs in some other charac- 

 ters from the corresponding organ of other Gasteropod embryos ; 

 that the superior oesophageal ganglion originates in the form of a 

 thickening of the outer germ-lamella (vertical plate); that the 

 primitive kidneys are composed of a few, not very large, perforated 

 cells ; that the foundation of the persistent kidneys stands in no 

 genetic relation to the ectoderm ; and, finally, that in some respects 

 the intestine possesses interesting peculiarities. The author has 

 endeavoured to bring these results into agreement with his previous 

 statements upon the development of Planorbis, and to show that the 

 same laws which had proved to prevail in the case of Planorbis 

 apply also to Bythinia, and that the differences result from the 

 greater abundance of nutritive vitellus which is presented by the 

 germs of the latter. — Anzeiger AJcad. Wiss. Wien, January 18, 

 1883, p. 13. 



