ZOOPHTTA. 221 



application of moisture, return to life. There is no doubt 

 but every inch of air contains the gerins of some of the 

 Infusoria in a dry state or their ova, and make up a portion 

 of that fine halo of dust which always appears in the air 

 when a gleam of sunshine is let into a dark place. 



The second class of the Eadiata, the Entozoa, are those 

 beings which inhabit, as parasites, the intestines and other 

 parts of animals. Their history is very obscure, but there 

 seems to be about twenty varieties of these creatures, and 

 a great number of animals have their peculiar Entozoa. 

 The best known in the human subject are the " Ascaris " 

 or thread-worm, the " Lumbricus Teres " or long- worm, and 

 the "Taenia " or tape-worm; this last is jointed, and grows 

 to several yards in length. 



The third class, the Zoophyta, includes four orders. The 

 first of these, the Hydroida, comprise the Tubularia, 



6 



PIG. 4 SEETULARIA OPEECULATA (a, Natural size, b, magnified). 



Sertularia (fig. 4), and Sponges (fig. 5) ; these are minute 

 gelatinous creatures, secreting a sort of tube in which they 

 dwell. These tubes are congregated into masses of different 

 forms and colours, and, with other structures totally different, 

 are erroneously known by the general name of " sea-weed." 



