SURFACE-SWIMMING FAUNA (INVERTEBRATES). 103 



There are no traces of wings on its thorax, 

 and it is therefore incapable of flight. Very 

 little is known at present of its development, and 

 practically nothing of its internal anatomy, so 

 that its proper position in the order of the Bugs 

 or Hemiptera is a matter of conjecture, but it is 

 an interesting little creature, in the fact that it is 

 the only member of its class that has a purely 

 pelagic life-history. 



Among the microscopic forms of life found in 

 the Plankton of the sea, the Radiolarians and 

 Foraminifers are perhaps the most important. 

 The Radiolarians are very minute specks of pro- 

 toplasm, usually protected or supported by an 

 elaborate skeleton of a substance closely allied to 

 flint. The form of this skeleton varies so much 

 in the numerous species that have been described, 

 that it is quite impossible in a few words to give 

 an adequate idea of the principal types. (See 

 Fig. 2). We may say, however, that in a con- 

 siderable number of them the skeleton has the 

 form of a hollow sphere, perforated by numerous 

 round holes and supporting outside a number of 

 long thin needles, The anatomy of the Radio- 

 larians is extremely simple. Their bodies are built 

 entirely of protoplasm which performs all the vital 

 functions. There is no definite head, mouth, 

 brain, nor muscular organ. This being the case, 

 the question arises, How do these animals pro- 

 vided with a skeleton of such a heavy substance 

 as flint manage to support themselves in the water 

 without muscular appendages 1 The answer to this 

 question is two-fold In the first place, the ela- 

 borate form of the skeleton presents an enormous 



