340 J. STANLEY GARDINER. 



32-5 grams were found in the mouth or first part of the gut, there remaining for the rest of the 

 intestine 220'5 grams of very coarse sand and fragments. A single, rather larger specimen, 

 taken while evidently still feeding, had 190-7 grams of sand. Five other specimens, also taken 

 in the early morning, extruded in the first 12 hours 47-9 gi-ams of mostly fine matter. In the 

 following night the coarse sand began to be got rid of 49-4 grams being weighed making 

 97'3 grams for the first day. In the second day 121-4 grams were extruded, in the third 

 99-3 grams, in the fourth 67 grams and in the fifth 22-5 grams. The experiment was then 

 concluded, 31-7 grams being weighed from the guts of the specimens, making a total weight of 

 sand of 439-2 grams. 



The specimens, recorded above, were obtained in fine weather in August, but of 5.5 specimens 

 examined on July 6, 1899, after bad weather of some days duration, 19 had no sand in the gut 

 at all, and only 18 of the remainder in the anterior part, showing that they had been 

 feeding. The experiments required an accurate means of dividing the sand into its differently 

 sized constituents. As it is, they merely show that the coarser particles are retained in the 

 gut — being necessarily to some extent reduced in size — and also that there is in certain 

 species a continuous passage of fine matter down the gut, presumably along its ciliated fold or 

 groove. The latter or some similar organ is characteristic of most true sand-feeding animals, 

 and probably in all cases functions in the same way. 



Of other Echinoderms the Echinids' are also true sand-feeders, the gut in most forms 

 being generally choked up with sand or small rock fragments. These animals, however, are 

 of no gi-eat importance on coral reefs, the most numerous forms living on the reef flat, 

 boulder zone or between branches of corals. Echinomus cijclostomus was found in some quantity 

 in the sand of the flat at Hulule. The adaptation of the sub-order to this mode of feeding 

 is seen in the animals possessing a fuiTow to the intestine or one or two siphons, which 

 undoubtedly subserve the same function as the groove in Holothurians. 



Ptychodera is also of great importance as a sand-feeder, though how far it actively 

 triturates the sand— considering its feeble musculature — is dubious. The presence of ciliated 

 grooves in the hepatic and abdominal regions of the gut indicates that the sand may be 

 for some time retained, when some breaking down would be sure to be accomplished. The 

 ejection of the sand is a rapid process, only taking a few minutes — all the species live in 

 the sand, some having burrows of poor construction — and occurs at the surface, the animal 

 at least in P. carnosa" slightly extruding its cloaca. No autotomy — so far as I have seen 

 from the examination of several hundred castings — takes place in nature. The animal after 

 ejecting its sand retreats again, but in P. flava and in P. cariiosa still carries with it more 

 than two-thirds of its original amount of sand. Further P. flava, if not irritated, retains 

 its sand for a long time, attempts to keep the animal, until it had cleaned itself naturally, 

 being quite futile for 4 days. 



The importance of Ptychodera, where found at all, lies in its great abundance. The 

 surfaces of sand flats throughout the Maldives are studded with the castings of P. carnosa, 

 often 100 c.c. or more of sand. As Dr Willey said of them in the S. Pacific, " they form an 

 important feature of the landscape at low tide^" Even more abundant in the sand of the 

 lagoon at Minikoi was P. flava, but its distribution in the Maldives was local. Where it 

 occurred, however, a single handful of sand was often found to contain 4 or 5 specimens. 



' See Prof. Jeffrey Bell's Report on the Actinogonidiate the collection, for the names of these species. 

 Echinoderms in the same Part of this Publication. ^ " Enteropneusta," Willey's Zoological Results, p. 256 



- I am indebted to Mr K. C. Punnett, who is working out (1899). 



