FEEDING OF CREPIDULA. 445 



a sedentary life, so that after settling down the animal must feed on 

 whatever food happens to be in its immediate neighbourhood. 



From my studies of the habits and anatomy of this sluggish animal 

 I had formed a hazy idea that, since the gut is very strongly ciliated 

 throughout, food was probably drawn in at the mouth in a current 

 of water. As a result of this idea, I concluded that the radula in 

 later life was an obsolete organ which the animal possessed merely 

 as a heritage from its ancestors. On my expressing this opinion to 

 Dr. Allen, he pointed out that if Crepidula possessed an obso- 

 lete but well- developed radula, then the phenomenon appeared to be 

 a new one, which required to be carefully investigated. Subsequently 

 a careful examination was made of the gut contents of Crepidula, 

 and a comparison established between these and the ingested food 

 of the native oyster, Ostrea eclulis, taken from the same grounds, 

 namely, off the Essex coast in the Blackwater near West Mersea. It 

 may be here remarked that as Crepidula has spread so rapidly on the 

 oyster grounds off the Kent and Essex coasts as to become a nuisance, 

 it has become a matter of much importance to oyster farmers to have 

 definite information about its food. The examination made of the 

 gut-contents of these two animals revealed a close similarity in 

 the kind of food-material, as far as skeletal remains indicate, and 

 the identity of the most common forms of diatoms found in both 

 animals. The contents of the gut of both these animals are mainly : 



1. Sand-grains. 



2. Sponge-spicules. 



3. Diatom shells. 



4. A^'egetable debris, Eadiolarian, Foraminiferan, 



and Peridinian tests. 

 The most common diatoms* present in both animals are : 

 f Adinoptychus undulatus, Bail. 

 j- Paralia sulcata (Ehr.). 

 Navicula aspera, Ehr. 

 Cocconeis scutellum, Ehr. and a var. parva ? 

 Hyalodiscus stelliger, Bail. 

 Adinocyclus ralfsii (Wm. Sm.). 

 Among the less common, but, in the case of some of the larger, 

 equally important forms are several species of f Coscinodiscus, Nitz- 



* For the identification of diatoms, works by Van Heurck (3) and Gran (4) were 

 consulted. 



t It is not surprising to find these plankton forms amongst the food of these animals. 

 Both Crepidula and oysters were taken from depths of only a few fathoms and not far 

 from the shore. In such a situation as this the plankton will doubtless be much mixed 

 up with bottom-living organisms. 



