PELAGIC PLANT LIFE 381 



ably form the chief basis, and in the open sea practically the 



sole basis, of nutriment for all the pelagic animal life, as well 



as, through their pelagic forms, for the fauna of the sea-bottom. 



It is not, however, quite so certain that all the different algae 



are equally useful as food to the animals which live on plant 



stuffs. Brandt's chemical studies of plankton organisms have 



distinctly shown that nutritive value does not necessarily 



correspond to volume. Diatoms, with their long silicated 



setae, or with big bladder-shaped cells that merely enclose a 



thin layer of protoplasm along the inner side of the wall, have 



little nutritive value compared to the majority of the peridineae, 



in which most of the cell -chambers are full of protoplasm. 



The dry substance of diatoms, according to Brandt's analyses Chemical 



of plankton samples, chiefly ChcEtoceras, contains 10 to 11.5 per o? plankton 



cent albumen, 2.5 per cent fatty matter, 21.5 per cent carbo- samples. 



hydrates, and as much as 64.5 to 66 per cent ash, 50 to 58.5 



per cent of this last being silicic acid. Another sample, largely 



consisting of Ceratium tripos, had a totally different composition, 



the dry substance containing 13 per cent albumen, 1.3 to 1.5 



per cent fatty matter, 80.5 to 80.7 per cent carbohydrates 



(half of which was chitin), and not more than 5 per cent ash. 



We are still without systematic studies of the nutriment of 

 plankton animals, and consequently do not know for certain 

 whether some families of plants are preferred to others. The 

 contents of the intestinal canals of salpse make it evident that ^ooAoi Saipa. 

 these animals at any rate collect all the different small organisms 

 to be found in their neighbourhood. In warmer waters the 

 greater part of. their stomach-contents consists of coccolitho- 

 phoridae and other tiny forms, but we find besides representatives 

 of all the plankton-algae. Small peridineae, for instance, like 

 Gonyaulax poly gramma, are seldom wanting. In fact, Stein, the 

 well-known specialist on protozoa, who had no plankton-catches 

 to aid him in his researches, got the best part of his material 

 from the stomachs of salpae, and was thus able to write his valu- 

 able initiatory monograph on peridineae. And this, too, was the 

 plan adopted at first for studying diatoms, so that our knowledge 

 of pelagic genera like Asteroinphalus and Asterolampra is largely 

 due to the examination of the stomachs of salpae. During 

 the cruise I invariably examined the stomach-contents of 

 salpae, and obtained thereby plenty of small forms, coccolitho- 

 phoridae especially, for comparison with the material in the 

 centrifuge samples. As we approached the coast of Europe, 

 however, the contents took on another character, for at Station 



