433 
The second theory is that proposed by Piitter (0S). He holds that 
the nutrition of many aquatic forms is essentially different from that of 
land animals. He shews that water contains large amounts of Carbon com- 
pounds in solution and demonstrates experimentally that this is the source 
of nutrition for a sponge, Suberites domuncula and a holothurian (Cu- 
cumaria grubei). In this paper and two subsequent ones, he extends his 
theory to include representatives of every phylum of aquatic animals. 
Possibly foreseeing the difficulty offered by the fact that in general, 
waste compounds of animals are less complex than their food, he sug- 
gests that a photochemical process may take place in aquatic animais, 
analogous to that of chlorophyl bearing plants. “Ob die gelésten Stoffe, 
die den niederen Tieren als Nahrung dienen, soviel Hnergie enthalten, dasz 
der Abban durch Spaltungen und Oxydaticnen allein hinreicht, um den 
Wnergiebedarf der Tiere zudecken, oder ob hier in einer weiteren Analogie 
mit dem Stoffwechsel der Pflanze strahlende Energie ausgenutzt wird, win 
durch photochemische Prozesse aus den aufgenommenen gelésten Stoffen 
Substanzen yon héherem HEnergiegehalt herzustellen, das ist eine Frage vou 
so hoher prinzipieller Bedeutung, dasz, die wenigen Hrfahrungen, die zu 
ihrer Hrérterung gegenwiirtig beigebracht werden k6nnten, nicht hin- 
reichend zur Entscheidung sind.” 
With the exception of Simocephalus vetellus, the methods of Ptitter 
have not been applied to species found in this pond. Wolff, ’09, was able 
to show that Simoccphalus vetellus could develop in a medium free from 
nutrition in the form of solids (geformte Nihrung). 
Without Genying the possibility that aquatic animals derive some food 
from the water by direct absorption of nutrient solutions, it may be stated 
with certainty that the higher animals of this pond for the most part 
utilize solid food. ‘This statement is based on observations on feeding and 
the examinaticn of alimentary tracts. 
In this discussion of the food relations of these animals, I shall ignore 
Piitter’s alternative. If it be subsequently proven that the ingestion of 
food is merely incidental, it will also establish their complete independences 
so far as food relations are concerned. 
I have tried to express in the accompanying diagram some of the im- 
portant food relations between the organisnis of the pond. ‘These relations 
are very complicated because of the omniverous habits of some of the 
[28—26988] 
