64 HOW TO USE THE MICROSCOPE 



material containing them is best sorted and examined 

 at home. Foraminifera also occur as fossils in 

 limestone and chalk deposits. 



Allied to the foraminifera are the Radiolarians, 

 which live in the plankton on the surface of the sea. 

 They differ from the foraminifera in that their many- 

 formed shells are composed of siliceous or flinty 

 material. They, too, are punctured, but with larger 

 holes. They are also obtained in fossil forms, and 

 are much prized by microscopists on account of 

 the beautiful appearance they present under dark- 

 ground illumination. 



The Corallines commonly found attached to sea- 

 weed and other substances are exceedingly interest- 

 ing live objects. As a type, we consider the Knotted 

 Thread Coralline {Obelia geniculata) which occurs on 

 seaweed near low- water mark. The stem extends 

 to about 1 inch, and is sometimes branched ; it is 

 easily recognized by its zigzag form. Examined in 

 a glass trough, in sea water, under a low power, we 

 see that the coral-hke stem gives off a series of cups, 

 each one of which is occupied by an animal armed 

 with tentacles. It is interesting to note that in 

 summer these " zooids," as they are named, give 

 rise to tiny medusoids, or swimming bells, which 

 produce eggs from which new colonies of Ohelia 

 develop. This species of coralline is phosphorescent. 



The serious worker will not satisfy his mind by 

 passing lightly from the examination of one object 

 to another. On the reverse, he mil seek to know the 

 hfe-stories of the creatures he observes, to under- 

 stand their anatomy and physiology, and to be able 

 to classify them in scientific fashion. 



