The Hog Louse 697 



from the background only with considerable difficulty. At six hours 

 the nuclei of the leucocytes show the first signs of disintegration, while 

 at eight hours the whole has an amorphous appearance and the hemo- 

 globin is disappearing. 



i In accordance with their parasitic habit, hog lice probably draw blood 

 from their host at frequent intervals and in small quantities; so that in 

 any one specimen taken at random and fixed and sectioned, all stages 

 of digestive activity will probably be found in the length of the mid- 

 intestine. Those fed to repletion in captivity showed absorption taking 

 place, as it were, in a gradual succession throughout the canal; and 

 even in these cases, not only have one or more cells in a state of active 

 secretion been found scattered among the absorbing cells, but absorption 

 and secretion have been seen taking place at one time in the same cell. 



THE FAT BODY 



In both larva and adult the hog louse is richly supplied with fat cells 

 arranged in a more or less definite plan. In the head they lie along the 

 lateral regions among the muscles and are most numerous toward the ven- 

 tral surface. There are also two small clusters dorsad of the sub-esophageal 

 ganglion just behind the brain. On the dorsal surface of the thorax a 

 cluster of fat cells lies above the occipital apodeme, while on the ventral 

 surface, between the ganglia and the hypodermis, lie four compact, grape- 

 like clusters which extend laterad to the coxae. In the abdomen, with 

 the exception of three clusters on the dorsal surface in the region of segments 

 5 and 6, the fat cells are not arranged in compact groups but are more 

 widely spread in dorsal and ventral peripheral layers. They are more 

 numerous among the lateral abdominal muscles than among the viscera, 

 particularly in the female. In the male these lateral cells are crowded 

 between the blocks of muscle and the body wall in the neighborhood of 

 the spiracles. 



In gross dissection the fat cells can be removed in clusters held together 

 by a rich network of tracheae. They are large, subcircular cells whose 

 wall is a transparent membrane through which the granular content is 

 clearly seen. In sections (Plate LXII, 10) the cells are seen to contain a 

 variable nimiber of nuclei, each with an oblong-ovate nucleolus surrounded 

 by a clear zone in which are scattered chromatin granules of varying 



