1897. NOTES AND COMMENTS. 295 



found in the Sogne Sea, on the West coast of Norway, prefaced by 

 a general survey of the invertebrate and tunicate fauna of the same 

 locahty. This is succeeded by a more detailed account of certain 

 nudibranchiate Mollusca, among which a supposed variety of 

 Tvitoma pleheia receives particular attention. The author nowhere 

 considers the possibility that his " colossal variety " is simply a young 

 specimen of Tntonia hombeygii, a view which is nevertheless rendered 

 extrem.ely probable by his figures and description. 



Professor R. Collett gives a detailed description of the interest- 

 ing deep-bodied Scomberoid fish Ptevycombus bvama, with beautiful 

 figures both of the external aspect and the skeleton. 



In a systematic note on the holothurians of Norway, Mr. Hj. 

 Ostergren confirms the view already expressed by Theel, that the 

 supposed spicule-less form named Holothuvia ecalcarea by Sars has 

 lost all its calcareous structures through the action of acids. It 

 appears to be a Stichopus closely allied to, if not identical with, 

 S. tremuhis. It follows from Ostergren's researches that our common 

 British cotton-spinner is the only true Holothuvia found beyond the 

 two 50th parallels of latitude. 



There are also in the Aarbog a systematic review of the 

 Collembola of Norway by O. J. Lie-Pettersen, faunistic researches in 

 Osterfjorden by A. Appellof, and a study of the eyes in Pecten and 

 Lima by K. E. Schreiner. 



The Eyes in Pecten and Lima. 



In Pecten, and indeed in many other animals whose eyes are even 

 better known, the relation of the nerves to the retinal cells is still in 

 dispute. According to Patten, a nerve-fibril runs axially through the 

 rod-cells and rod, emerging at the tip of the latter in order to bend 

 back over its outer surface, which is thereby covered with a compli- 

 cated network of fine nerve-endings. Mr. Schreiner denies the 

 existence of any such axial nerve or canal, but maintains that the 

 appearance is produced merely by the shrinking of the cells so as to 

 form longitudinal ridges, while the axial thread that is to be seen in 

 the rod itself is, according to him, merely the continuation of the 

 protoplasm of the rod-cell. Patten's statement that the outer ends of 

 the rods project slightly through a definite, perforated membrane, 

 which he calls the " vitreous network," though rejected by Rawitz, is 

 confirmed by Mr. Schreiner, who further supports Patten in his view 

 that the rods are not, as maintained by Carriere, embedded in a fatty 

 substance, for such an appearance is easily produced by reagents. 

 External to the rod-cells are the ' ganglion cells,' which, over the 

 central region of the retina, are in three or four layers, but at the 

 periphery form only a single layer. The optic nerve, as is well known, 

 branches, one branch going to the proximal base of the eye, the other 

 running laterally past the retina in order to bend round on to its 

 distal surface. Here the retina, says our author, is covered by a 



