THE CRYSTALLINE STYLE OF LAMELLIBEANCHIA . 597 



one the right and rlie other the left compartment. They 

 are open at both ends : but tlie stomach-ends of both are 

 guarded by a cuticuLir value. It is in the left compartment 

 that the style is lodg-ed. Now what is the use of the right 

 compartment ? It took me some time to find out. It is 

 through the right compartment tliat food material is, as a 

 rule, passed on from the stomach into the rest of the alimen- 

 tary canal. By careful dissection of the animals when they 

 are digesting food actively, one can see witli the naked eye 

 particles of food material forming a very slender cord (figs 

 1 , 8), and being hurried along through this compartment by 

 the action of the cilia. It is easy to see tliat if there were no 

 such division of the lumen into compartments (here would be 

 no proper storage of the ferment, and food material might be 

 passed on without being properly mixed up with the ferment. 

 It is not out of place to mention here that the caecal 

 diverticulum in Pholas that lodges the crystalline style 

 arises from the same point of the stomach aa the intestine, 

 that it runs ])arallel with the first portion of the intestine, 

 and that it is placed to the left of tiie same portion (fig. 9). 

 These facts with regard to the point of origin and the position 

 of the cfecum in Pholas, coupled with the undoubted fact 

 tliat Pholas is a more highly specialised form than Anodon, 

 and the fact mentioned above, that the crystalline style when 

 it is lodged in a ctecum is completely free from food particles, 

 Avhereas, when it is lodged in the alimentary canal itself 

 food particles are occasionally found in its substance, force 

 the idea on one's mind that this blind caecum is only a 

 differentiated part of the first portion of the intestine, and 

 that it has been evolved from the left compartment of the 

 first portion of the intestine of Anodon by the permanent 

 coalescence of the ciliated ridges and shntting up of the 

 distal end of the compartment. It is to be remembered liere 

 that this phenomenon — viz. the permanent coalescence of two 

 ciliated surfaces — must have taken place extensively and over 

 and over again in the evolution of the more complicated 

 forins of the Lamellibranch gill-plate, 



