60 J. Wood -Mason — Scent -glands of Thehjpliomis. [MakCH, 



and tubular organs of huge size, extending from the 19tb somite ol: the 

 body (on wliich they open by two minute valvular apertures placed at the 

 sides of the anus) to the front end of the 13th in the male, but to the 

 ■ middle of the 11th in the female (whose glands are consequently the 

 larger), and being, with the exception of the voluminous liver, the most 

 conspicuous of the viscera. They are two subpellucid bags shaped some- 

 what like an Indian club, striped longitudinally with white, and filled to 

 distension with a thin and clear fluid. They are not quite equal nor are 

 they placed symmetrically in the body-cavity, but the one or the other lies 

 between the nervous chain and the ventral body wall in the middle line 

 between the two rows of vertical muscles, and the other between the row 

 of muscles and the lateral wall of the side of the body to which it properly 

 belongs. They apparently consist of a strong and structureless basement 

 membrane invested externally by a layer of delicate striped muscular fibres 

 arranged circularly and of an inner membrane ; the walls of the short 

 (1 mm. long) ducts are transversely thickened so as to resemble the 

 tracheae of insects ; the glandular tissue is arranged between the two 

 membranes in longitudinal plaited stripes so as to permit of the expansion 

 of the lumen of the tubular organ into a receptacle or bladder for the 

 storing up for use of the secreted fluid, to which apparent arrangement of 

 the glandular substance the striped appearance of the organs is due. 



The secretion doubtless serves to protect the animals from attack, and 

 it is interesting to find that the female in this, as in so many other animals 

 which are similarly protected by their offensive odour, is, as being for 

 obvious reasons the more important sex, more perfectly protected than the 

 male by having, not indeed, so far as could be detected, a stronger and 

 ranker, and therefore more disagreeable scent, as in many insects, but 

 larger scent-secreting glands. Another point of interest brought out by 

 this investigation is that the two glands exhibit a tendency to coalesce and 

 form a single unpaired median organ, the two being always unequal and 

 occasionally partially united and the one in the middle line invariably 

 the larger. 



These structures seem to belong rather to the category of excretory 



organs than to be highly developed skin-glands ; and they are probably 



homologous with the silk-glands of other Arachnida and of Insects, with the 



green-gland of the Crayfish, and with the segmental organs of Worms and 



Peripatus. 



2. On the Structure of the * Foot' in certain Terrestrial Gasterojpoda. — 



By J. Wood-Mason. 



(Abstract.) 



In this paper the author describes the structure of the part of the 

 foot called by German writers on Malacology the ' I'usssaum,' which, as no 



