252 Dr. T. Williams on the Mechanism of Aquatic 



The author's purpose at present is simply to present a sketch 

 of the structure of these glands. No opinion with reference to 

 their function can assume a stable and reliable form which is not 

 supported by the results of other researches into the structure 

 of the corresponding organs of other classes of invertebrate 

 animals. This more extended task is reserved for another 

 occasion. 



Although in Limax the so-called '^ muciparous gland" differs 

 both in ligure and situation from that of Buccinum, in minute 

 structure they are not only similar but identical. The folds of 

 which these bodies are composed were called the " feuillets 

 muqueux " by Cuvier. They are attached to the internal face of 

 a sort of a tunica propria, by which the entire gland is closely 

 bound down. This tunic, regarded in its length, forms a 

 cylinder. The axis of this cylinder is an open space. The 

 sides bear the glandular folds. A transverse as well as a longi- 

 tudinal section of the gland is required in order to display the 

 true disposition of the glandular laminae. 



These bodies are richly ciliated both within and without. 

 Each fold ends in an excretory duct. The ducts emanating from 

 each fold are tributary to a common duct which runs along the 

 axes of the gland and joins the rectum at different points in 

 different genera. This fact, which can be readily veriticd, is 

 worthy of remembrance. From this fact alone the conclusion 

 is beyond dispute, that if these glands be the real bodies by 

 which the "mucosity^' with which, almost at will, the respira- 

 tory cavity in these animals may be tilled, it can only attain this 

 cavity by oozing through or transuding the tunica propria of the 

 gland, — a conclusion repugnant to reason, and at variance with 

 all physiological analogy. 



In Buccinum the gland is flatter and less cylindrical than in 

 Limax. This occasions a slight difference in the mode in which 

 the laminse (fig. 8 a) are attached to the tunica propria. It is by 

 no means difficult to detach a single fold («) in a perfect state 

 and place it under the microscope. By this simple expedient 

 the entire machinery of this gland is rendered at once evident. 



A highly ciliated membrane, more delicate than, although the 

 prolongation inwards of, the tunica propria, gives its form to, 

 and contains the gland-substance of, this fold. The external 

 surface of this membrane, although within the boundary of the 

 tunica propria, is not the true interior of the gland. The true 

 interior spaces of the gland communicating with the duct are 

 not ciliated ; nor is the internal surface of the rectum in which it 

 terminates. It will be seen that the entire mass of the glandular 

 fold or lamina under examination consists of two elements : 

 first, the Florence-flask-shaped vesicles (fig. 8 b, h, and B, h). 



