64 THE PROTOZOA 



tion for developmental changes, especially in the female gamete, 

 in a manner analogous to yolk-grains in an ovum. Instances of 

 bodies resulting from catabolic activity are waste-products of various 

 kinds in the form of granules, crystals, pigment-grains, etc., often 

 present in great numbers, and giving the endoplasm an opaque and 

 coarsely-granular appearance. A familiar instance of such waste- 

 products is seen in the grains of melanin-pigment formed in the 

 bodies of the malarial parasites (Fig. 156) as a result of the absorp- 

 tion and decomposition of the haemoglobin of the red blood-cor- 

 puscle. 



Many bodies present in the protoplasm of Protozoa may be con- 

 sidered as originally of metaplastic nature and origin, but as 

 utilized secondarily for various functions. Such are the oil-drops 

 in the intracapsular protoplasm of Radiolaria (p. 251), which appear 

 to have a hydrostatic function, and also to serve as reserve food- 

 material in the development. It is also highly probable that both 

 internal and external skeletons originated simply as excretions in 

 the first instance that is to say, as waste - products of the 

 metabolism which have been utilized for the function of support, 

 and subsequently adapted and modified in accordance with the 

 special requirements of the organism. 



Finally, as bodies of hydrostatic function, though not to be 

 included necessarily under metaplastic products, are the peculiar 

 gas-vacuoles of Arcella, bubbles of gas which can be secreted, 

 absorbed, and formed again, as circumstances may require, in and 

 by the living protoplasm. 



BibliograpJiy. For references see p. 47" 



