W. H. FURLOXGE OX THE PULEX IRRITAXS. 17 



Tlie posterior extremity of the digestiye sac is connected either 

 directly, or by a very short canal, with the anal orifice which opens 

 just behind the pygidium. 



Having thus described the structure of the alimentary and diges- 

 tive canal, and the organs pertaining to it, so far as I have been 

 able to make them out, I will now briefly recapitulate my views of 

 their functions. 



Tlie blood as ingested passes directly to the first stomach, which 

 appears to perfomi the office of a crop, or receptacle for the food. 

 In this organ it is, as we have seen, kept in a state of violent agita- 

 tion, and is, I believe, constantly regurgitated into the gizzard, 

 where it is submitted to the action of the corrugated iTibbing sur- 

 faces of that organ, the blood corpuscules being thus broken down. 

 From time to time, portions of the contents of the fii'st stomach are 

 expelled through the valve at the posterior extremity of the stomach 

 into the intestinal canal, connecting the two stomachs. I may 

 obseiTe, in parenthesis, that 1 have frequently had an* opportunity 

 of observing this passage of the contents of the first stomach into 

 the second, and that the successive portions of the contents thus 

 transferred, never rested in the connecting intestinal tube or gut, 

 which is always enij)ty except at the moment when the food is 

 passing through it into the second stomach. It is possible that 

 some portion of the blood may be taken up by certain quasi absor- 

 bent vessels with which the canal is seen to be lined, even in the 

 course of the rapid passage I have described, but without doubt the 

 chief portion of the assimilative process takes place in the second 

 stomach. This appears to be proved by the fact that when the 

 insect is permitted to gorge itself with food, it will, as already noticed,, 

 fill both stomachs with blood, and, of course, the contents of each 

 will present precisely the same appearances under the microscope ; 

 but after the digestive process has gone on for some time, the con- 

 tents of the second stomach (which, in the first instance, very 

 speedily assume an opaque dark brown colour) become progres- 

 sively lighter in tint, until at length the contents of the sac appear 

 to consist of a limpid fluid of a light red or pink colour, in marked 

 contrast with the deep crimson colour of the contents of the first 

 stomach, which, I may remark, almost always retains its crimson 

 colour so long as it remains in that organ. When the food has 

 been so far digested, the insect emits small portions of the contents 

 of the sac from time to time, as excreta, to make room for portions 



JouRN. Q. M. C. Ko. 18. c 



