46 CALIFORNIA ACADEMY OF SCIENCES. 



resemble the parents in essential characters; the notice- 

 able differences are the comparatively larger head, the 

 smaller, especially shorter, abdomen, and the absence or 

 incompleteness of the markings, especially those of the 

 abdomen. The color of the very young is always whit- 

 ish ; as they grow older chitinization follows and the brown 

 and black colors appear (see plates). The number of 

 moults or the duration of immaturity is not known for 

 any species. I have observed nymphs (presumably in 

 the stage preceding the final moult) which were fully as 

 large as the adults of the same species. I have figured 

 the immature stages for one or more species in nearly all 

 the genera met with by me on the water and shore birds 

 (see plates). In none of the monographic works is there 

 any attention paid to the young. From the preceding 

 brief account it is obvious that the life -history of the 

 Mallophaga is as yet practically unknown. 



Parasitism. The parasitic habits of the Mallophaga 

 have been the subject of some little study, mainly directed 

 to ascertaining whether or not the blood of the host ever 

 forms a part of the food of the parasite. From the con- 

 dition of the mouth parts and from repeated examination 

 of the contents of the crop the food of the Mallophaga is 

 affirmed to be the epidermal scales and the hair or feathers 

 of the host. The conspicuous large, dark, pear-shaped 

 blotch in the abdomen found in a majority of individuals 

 examined is discovered, on careful examination, to be the 

 crop and its contents, composed of bits of feathers show- 

 ing through the semi-transparent body of the insect. In 

 Nitzsch's drawings, illustrating the Insecta Epizoa, this 

 food-filled crop appears in many of the individuals figured. 

 Denny's figures also show the discolored crop. Of course 

 such a "marking" is an evanescent one: immediately 

 after a full meal it would be present: later, after diges- 



