68 MICROSCOPIC OBJECTS. 



portion of the wing is mounted in Canada balsam, re- 

 quire a power of 100 diameters. 



The wing cJ|i|Le Asilus crabroniformis when mounted 

 in balsam is a ireautiful example to illustrate the hollow 

 structure of the pterocosta, or wing-bones. 



The wings of the Phryganea are often covered with 

 stout hairs or bristles ; the base of these, as also the 

 pores or openings placed at intervals on the pterocosta, 

 are worthy minute examination. — Power 150 diameters. 



Zoophytes.- — ^Animal-plants usually inhabit the bottom 

 of the sea, where many of them perform an important 

 office in producing solid masses of hmestone, as exemplified 

 in the formation of coralline islands. Naturalists of the 

 Continent include in this class of animals not only the 

 Corallines and Sponges, but also many of the small Mol- 

 lusca, Entozoa, Star-fish, and even Infusory Animalcules. 



For a long period the zoologist did not consider zoophytes 

 as animals, but left the study of them to the botanist ; 

 and even now, many observers are disposed to class them 

 with plants, while others hold them as a link between the 

 two kingdoms. The animals are generally found in clus- 

 ters or compound, sometimes communicating at a com- 

 mon centre, at other times distinct and only connected by 

 the solid matter of which their polypidoms are formed. 

 Some few, as the common freshwater polj'pe, do not 

 secrete any hard substance either around or within them. 

 Those which are described and figured m the ' Notes on 

 Natural History' are excellent microscopic objects, and if 

 kept in cylindrical glass vessels of water are always ready. 



