FOOD OF THE OYSTER, CLAM, AND RIBBED MUSSEL. 379 
| 
, Average sample of the excrements of £4 clams, collected on the flats at the Soldiers’ Home, 
¥ Hampton, Va, 
Preparation No. 1. Preparation No. 2. || 
-. | 
| | Field Dead. Dead. | Results. 
| Lo SSS LS ap 
Col. I. | Col. IT. Col. I. | Col. IT. || 
1 1 7 2d 0 Yio NSaencecté | Results of Preparation No. 1: 
2 0 ee | Sa ee 0 | Me 5 sarSeas | Per ct 
3 0 ye all he a ga UN)! ate eal ESeE See TEA VAN Oona at aeration elaine 
4 0 Oryeiases. OLY Dieses Entirely digested.........--.-. 83 
5 0 3 iy el) a FAR ig Lee) es Nearly digested .......--..-.-- 15 
6 0 3 Oe vita Dik, eee 
ui 0 ee tara ad || 0 2 ld Note, 232s saeseee te ee 100 
8 0 3 als Weston Od pet AN hy [SSA BA: === 
9 0 3 ld CO Rag am See Results of Preparation No. 2: 
0 ie Oar) 0 4 Ivins ache sasae se eee eee ae 0 
0 By eae 0 4 Entirely digested.........-.--. 86 
0 PN: | 0 1 Nearly digested.......-.-..-.-- 14 
0 3 1d 0 0 —— 
0 eS eer 0 TAA |) Total 43. 260K ...VIrpaseeee 100 
0 Breas eae Git, -t--| = 
0 es allbeenses Oe Soe aioe ea Average: 
0 2 1d 0 PW enere see Di ested fa dates eesaacias 22 oee ae 99 
0 (ie 0 4 2d Hnitirely sins. goss 84.5 
0 Ye ee ae 0 2, pela | IN CATV EE Se ocn anatase 14.5 
0 i Weeseaobe 0 OT oddeceee | EVA Siete a ctee verate salto 1 
0 Dae iy Sve aul 0 lle PS Seehc re ae 
0 ip hi betaine 0 i la ea ed 8 otal sess ee see eee ese 100 
0 Hits lta. st 0 re Ae ene | 
0 ee aan t 0 1 1d | 
0 a eee 0 Di lai cok feparire 
1a 55—=464+9 || 0 43 —37+6 | 
* Probably derived from the sea water used to break up the excrements. 
There was another possible kind of food yet to be considered, 
namely, such substances as might be in solution in the water in which 
the oyster lives. The oysters attached to the stones of the Ripraps, 
which also showed their stomachs full of diatoms, are surrounded by 
perfectly clear water, but from a large number of chemical analyses 
which I have made of similar water on former occasions, after having 
Strained the diatoms, etc., out, 1 am convinced that hardly a trace of 
organic matter is to be found dissolved in it, so that this possible source 
of food can be entirely excluded. 
After having determined in this way that the food of the oysters 
and clams in the James River consists practically of diatoms, the 
‘question presented itself, Where do these diatoms come from? The 
use of the common Miiller’s pelagic tow net revealed their presence at 
the surface of the water in enormous quantities, and no difference 
could be detected in their numbers or distribution during the daytime 
or nighttime. The occurrence of diatoms in such numbers at the 
surface explained well their presence in the stomachs of the oysters 
attached to the stones and piles submerged only a little under water, 
but this could not account for their presence in those living at the 
bottom in deeper places, where even at low tide considerable water 
remained. It was therefore thought advisable to collect at different 
depths in order to study their perpendicular distribution from the 
surface to the bottom. The result showed that they occurred in equal 
‘quantity at all depths up to 70 feet, which, according to the official 
naps, is the greatest depth found at the mouth of the James River. 
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