402 Quarterly Journal of Conchoiogy. 



the water and rising again for respiration ; but I have not suc- 

 ceeded in confirming this observatiou, and hive great doubts of 

 its accuracy."* 



Mr. Reeve does not teU us hov>' he proved his assertion about 

 the "hydrauhc action of the foot," and does not seem to have tried 

 to ascertain how they "hold themselves stationary at different 

 depths in the water,'' — cooUy "doubts" Montagu's statement 

 about the "mucous tliread," and does not notice Mr. Warington's 

 observations at ah. I may state that a moUusk is only capable of 

 "holding itself stationary at different depths in the water" when 

 attached to a thread, and that no "hydraulic action" of the foot 

 takes place. When a moUusk is forming a thread, the "lateral 

 margins" of the foot are brought together, forming a channel for 

 the natural flow of mucus down the sides of the foot to the tail; 

 thus n.dding to the thread, which is gradually extended. The 

 existence of a thread may be proved, as stated by ]\f r. Warington, 

 by passing a rod under the creature, by which means it can be 

 swayed to and fro. 



I have taken great interest in this thread-spinning, and long 

 before I had read Mr. Warington's excellent notes I had been 

 observing this seeming phenomenon, and had tabulated the species 

 absolutely seen by myself in the act, and noted the conditions 

 under which mollusks are capable of producing and using a thread. 



Let me here explain that the words thread and spinning are 

 used descriptively, and it must not be supposed that these threads, 

 or the production of them, bear any anology to the spinning of 

 spiders. In the case of the mollusk the thread is gelatinous — in 

 fact, is formed of the slime of the creature, the process of forming 

 it being, to a certain extent, an involuntary act, although it is 

 used for a set purpose; whereas the spider's thread is silken, and 

 its formation is entirely under the control of the creature. Neither 

 are they to be confounded with the byssal filaments of the Myiilidce, 



* Lovell Reeve, "British Land and Fresh-water Mollusks," pp. 150-1, 1863. \ 



