B94 MR, J. B. GATENBY ON THE BIONOMICS, EMBRYOLOGY, 



tracheae of the host and the muscles and connective tissue of its abdominal 

 cavity are untouched. 



The larvse when dissected out are transparent white objects, which are 

 incapable of very active movement. They are able alternately to contract 

 and relax the lateral muscles of each side of their body so as to produce a 

 slow wriggling movement. In all the larvse examined the terminal 

 abdominal body is seen to be specialized in that it is expanded to form a 

 bladder, which differs in size at different stages of the larva^s life. 



In PI. 24. fig- 3, a to h, are eight larvse drawn at a magnification of eight 

 diameters. At a is the smallest larva I found ; it is drawn at a much 

 greater magnification in PI. 26. fig. 16. The tail bladder or vesicle is not 

 externally conspicuous. Grradually as the larvse grow, the bladder becomes 

 larger and larger in proportion to the size of the other segments of the body, 

 till as in PI. 24. fig. 3, e and/, it becomes a remarkable object. From the 

 stage in / the bladder no longer grows any larger, and soon afterwards it 

 begins to become absorbed (^). By the stage in h, it is only a small 

 projection at the ultimate segment of the body, and when the larvse are full- 

 grown and ready to bore their way outside the body of their host, the vesicle, 

 while still demonstrable, is very small — its part has been played (see text- 

 figs. 1 & 2) ; the larvse pupate in the ordinary way, and I could find no 

 sign of the vesicle after examining the externals of a number of pupse. 



c. The Anatomy of the Larvce. 



The number of segments in the larva is a most difficult matter to ascertain. 

 Seurat thinks that altogether there are thirteen, counting head and terminal 

 vesicle. In the young larva drawn on PI. 26. fig. 25 there were fourteen 

 segm.ents, counting head and vesicle. The same seemed to be the case with 

 all the larvse I could examine. I believe that there are, one head, three 

 thoracic and ten clear abdominal segments — counting the bladder as a 

 segment. Seurat's figure gives nine abdominal segments, counting the 

 bladder. I think Seurat may have made a mistake, for I have made very 

 careful observations specially to solve this question (see also p. 400). 



The head, thoracic and first nine abdominal segments are quite normal ; 

 " segment ten " of the abdomen is inserted into the ninth by a " bottle- 

 stopper " joint. This can be seen in PL 25. fig. 10 and PI. 26. fig. 25. In 

 the embryonic larva the tenth segment is larger than any of the other 

 abdominal segments, and its walls are very thick (PI. 26. fig. 25). 



d. The Alimentary Tract is very peculiar. It is entirely made up of 

 hypertrophied cells. The oesophagus and buccal mass (BM., PI. 24. fig. 6) 

 are normal ; there is an oesophageal valve, which is poorly developed, but 

 the oesophagus does not lead straight into the mesenteron (mid-gut). In all 



