ZOOLOGY AND BOTANY, MICROSCOPY.. ETC. 189 



type, rock-haunters, sand-dwellers, &c, being all well represented. It 

 would thus appear that the actual bottom deposit is of less importance 

 as a determining factor than such characters as absence of currents, 

 specific gravity of water, percentage of organic matter, &c. The fauua 

 shows an intermixture of northern and southern forms, the latter being 

 about twice as numerous as the former. 



Among the Nudibranchs a form occurred similar to the species of 

 Corambe but without the anal notch, and therefore placed in Corambella 

 g. n. as G. depressa sp. n.] 



y. Gastropoda. 



Glycogen in Snails and Slugs.* — Dr. Charles Creighton, in the 

 course of his investigations on glycogen, has studied it in Invertebrates 

 generally, and finds that it is abundant in Mollusca, especially the Pul- 

 monata. In them it occurs in the "plasma-cells" of Brock which are 

 so characteristic of these auimals. These cells surround both the arteries 

 and the venous sinuses, constitute a peritoneal endothelium, form a 

 sheath round the nerves, and also occur in connection with the muscles. 

 The author regards them as constituting a prototype of the lymphatic 

 system of Vertebrates. Morphologically they may be compared to the 

 glycogen-containing cells found investing blood-vessels in the embryo 

 chick, which become actual lymphatic cylinders. Again they can be 

 shown to be physiologically the equivalents of the Vertebrate lymph 

 system. 



Origin of Asymmetry of Gastropods, f — Prof. Karl Grobben has 

 always been of opinion that the deep-seated torsion of the Gastropod 

 and the superficial coiling of the viscera stand in intimate causal rela- 

 tion to one another. This is indeed the position which has been held 

 by the majority of authors ; it is the question as to which is cause and 

 which is effect which has given rise to so much discussion. After 

 summarising the views of others up to date, the author proceeds to the 

 statement of his own conclusions. In the first places, he correlates the 

 anterior position of the anus to the possession of a shell (cf. Biitschli and 

 Lang) ; such cases as Phoronis, the Polyzoa, and Sipunculus, showing 

 that this anterior position is a necessary adaptation to life in a tube or in 

 sand. But in the Gastropod body there are, as it were, two points of 

 fixation, the dorsal attachment of the visceral hump to the shell, and 

 the ventral attachment of the foot to the substratum. In consequence, 

 the shifting of the anus can only take place laterally, and its movement 

 involves a twisting of the pallial complex. This usually takes place to 

 the right, but may exceptionally be left-handed, and involves the pro- 

 duction of asymmetry in the visceral hump. The spiral coiling of this 

 is in the first place determined by an increase in size of the mantle 

 cavity and of the visceral hump, and is favoured by natural selection 

 on mechanical grounds. These views are illustrated by figures showing 

 stages in these structural modifications, and lead to the conclusion that 

 the ancestral Gastropod had a large visceral hump and a creeping sole. 

 The deep-seated torsion and the spiral coiling arose simultaneously as 

 the visceral hump increased in size. 



* 'Microscopic Researches on Glycogen,' part ii., London, 1899, 127 pp., 9 pis. 

 t Arbeit. Zool. Inst. Wien, xii. (1899) pp. 25-41 (8 figs.). 



