Respiration in Invertebrate Animals. 251 



of form and place and size, in all the pectinibranehiate and 

 pulmonated Gasteropods. Under all diversities, it is identifiable 

 by its anatomical structure. Cuvier thus defines its oftice and 

 locality : " Le rectum, et oviductus de la femelle rampent aussi 

 le long du cote droit de cette cavite, et entre eux et les branchies 

 est un organe particulier compose de cellules recelant une 

 humeur tres-visqueuse, servant h former une enveloppe com- 

 mune, qui renferme les oeufs et que Tanimal depose avec eux*/' 

 That gland which in Bvccinum is situated between the rectum 

 on the right and the branchia on the left (when the roof is in 

 situ), and attached to the roof of the branchial chamber, is the 

 same gland with that which in Limax niger (fig. 1 c, c) lies on 

 the floor of the pulmonary cavity, is extended in figure, and 

 circumscribes a space in the centre of which the heart is situated. 

 These two examples will serve to indicate the extremes of figure 

 and locality which one and the same gland may assume even in 

 kindred genera. 



In the Littorinidse (fig. 7 f) it afiects the same position on 

 the roof between the branchia and the rectum. 



In the Helicidse (fig. 3 g) it appears under the form of an oval 

 mass, situated still on the roof of the pulmonary cavity; and, 

 when the parts are in situ, to the right of the heart. Thus in 

 the particular of locality, this gland in Helix difi"ers remarkably 

 from that of Limax, in which it is placed on the floor (fig. 1 c, c) 

 of the cavity. In the Lymneadse it is observed to occupy the 

 same situation as it does in the Helicidse. The Planorbidse are 

 too small to render it practicable to examine this gland separately; 

 but, as in the former family, its position is on the roof and on 

 the right of the heart. 



That gland which by Dr. Sharpey has been called the supple- 

 mentary and doubly laminose gill, is a totally difierent organ 

 from the former. It does not exist under any form in the 

 pulmoniferous orders. It is largest and most developed in 

 Buccinum ; in the Periwinkle it is also very distinctly observable. 

 It is situated always to the left of, and parallel to, the branchia. 

 It is invariably tinged with a dark green colour. It terminates 

 anteriorly in a long excretory duct which travels under the 

 membrane of the vault and ends near the rectum. 



By Cuvier, and all systematic naturalists, it is believed to be 

 the organ which secretes the " purple and other dyes " which 

 these animals are capable of pouring out, and has been ac- 

 cordingly designated the " colour-gland.^' In relative position 

 and in general and minute structure, it is readily distinguishable 

 from the " organe de la mucosite '' of Cuvier. 



* Regne Animal, vol. sur les MoUusques. 



