490 SUMMARY OF CURRENT RESEARCHES RELATING TO 



of many marine molluscs (Haliotis, e. g.). Very frequently the peri- 

 podium is provided at its posterior extremity with a capacious pit, the 

 capacity of which may he increased by the prolongation upwards of 

 its anterior margin in the form of a horn, which not being specially 

 sensitive is not a tentacle, often it is without this terminal pit ; it is 

 invariably richly ciliated throughout from the mouth on one side 

 round to the mouth again on the other side dorsally; equally in- 

 variably is it limited off from the side of the body (and frequently 

 also from the muscular foot) by a peripheral groove, which deepens 

 anteriorly. Its office is to assist in lubricating the foot, the pit when 

 present receiving the effete lubricating fluid and throwing it off in 

 gelatinous lumps. 



The foot-gland, as is well known, pours out its abundantly and 

 constantly flowing secretion through an aperture which is situated 

 below and a little behind the mouth into a hollow whence it naturally 

 falls into the deep anterior end of the dorsal peripheral groove, whence 

 again it is carried by the cilia with which the surface of the peri- 

 podium is beset (being distributed to the foot as it goes) to the 

 terminal pit. In those forms in which this pit does not exist, the 

 secretion that has served for lubrication is merely left behind by the 

 crawling mollusc. 



As Pulmonata possessing a ciliated peripodium with and with- 

 out a terminal pit are to be found in every quarter of the globe, and 

 as it is in the highest degree improbable that so highly specialized 

 a structure, subserving such an important purpose in the animal 

 economy as this evidently does, has arisen independently many times 

 in many different forms in many widely separated areas of the earth's 

 surface, the author considers that it has a higher taxonomic value 

 than has hitherto been assigned to it, and he feels strongly inclined to 

 distinguish those forms that possess it and those that do not (or 

 have lost it) from one another by calling them Craspedophora and 

 Lipocraspeda respectively. 



Mucin of Helix pomatia.* — According to H. A. Landwehr, when 

 the mucin of Helix pomatia is treated with 1 per cent, sulphuric acid, 

 it yields grape-sugar, whereas mucin from other sources yields only 

 a reducing substance. The grape-sugar cannot be derived from 

 glycogen, since the iodine reaction fails entirely in the freshly 

 expressed secretion, and in the mucin prepared from it. The author 

 however, succeeded in obtaining a carbohydrate, for which he proposes 

 the name " achrooglycogen." In order to prepare it, he directs that 

 the mucin obtained from the snails shall be treated with 5 to 10 per 

 cent, caustic potash, and the proteids separated by Brucke's solution 

 (potassiomercuric iodide), the solution filtered, and the filtrate pre- 

 cipitated by alcohol. The material thus obtained, after being washed 

 with absolute alcohol and dried, is an amorphous, white, tasteless 

 powder, readily soluble in water. The solution is strongly opalescent, 

 gives no iodine reaction, and does not reduce an alkaline coppei 



* Zeitschr. f. Physiol. Chem. ? vi. (1882) pp. 74-8. Cf. Journ. Chem. Soc. 

 Abstr., xlii. (1882) p. 708. 



