144 JOHNS HOPKINS UNIVEESITY MORPHOLOGICAL MONOGRAPHS. 



in sufficient numbers to be compared with those of the land, and the 

 food of the copepods is only partially vegetable, for they devour micro- 

 scopic animals as well as microscopic plants, and probably to an equal 

 amount. 



The group Crustacea as a whole is a carnivorous one, however, for 

 while a few subsist on algas, their number is inconsiderable. Others 

 chew the mud of the bottom and extract its organic matter, but this is 

 chiefly animal and consists of foraminifera and rhizopods and infusoria. 



The molluscs as a whole are carnivorous, and while there are many 

 exceptions, such as the nudibranchs for example, many nudibranchs 

 feed on hydroids. 



The cephalopods and pteropods and heteropods and many of the 

 gasteropods pursue and destroy their prey, and other gasteropods are 

 scavengers, while the lamellibranchs gather up the microscopic organ- 

 isms which are drawn into their gills with the water. 



The majority of the worms and echinoderms are animal-feeders. 

 Some of them, like the common starfish, are actively predaceous; others, 

 like the crinoids, gather up microscopic organisms from the water; 

 others, such as most holothurians, eat the mud of the bottom and digest 

 out of it the foraminifera and small molluscs and annelids and crus- 

 tacea which it contains, while others, such as the sea-urchins of the 

 coral reefs, grind away and swallow the living coral. The universal 

 presence of a poisoning apparatus in the coelenterates shows that the 

 food of this great and important group of marine animals must consist, 

 in the main, of animals which are able to resist or to escape, and observa- 

 tion shows that this is true. Floating jelly-fishes and siphonophores are 

 often found fastened to the half-digested carcasses of sagittas or hetero- 

 pods or fishes larger than their captors, and they consume enormous 

 numbers of copepods, pteropods, young fish, and pelagic larvae of all 

 sorts. So far as we know, all the sea-anemones and coral polyps and 

 alcyonarians and hydroids are carnivorous. Some of the discomedusa3, 

 the rhizostomes, feed upon microscopic organisms, but this mode of life 

 is exceptional, and some recent observations, as yet unpublished, by Dr. 

 R. P. Bigelow, show that the food of the rhizostomes consists of cope- 

 pods. 



Except for a few plant-eating fishes and molluscs and worms and 

 echinoderms, all the animals of the ocean fall into two classes, those 

 which subsist on microscopic organisms, and those which prey upon each 

 other and correspond to the rapacious animals of the land. 



