602 Dr. D. Keilin on 



Mr. F. W. Edwards has suggested that the specimens 

 probably belong to the subfannly Eristalinse. 



In his note Baylis expresses some doubt as to whether or 

 not tl'.ese larvje can be actually parasitic ; he believes it is 

 possible that the larvte may have been living in the decaying 

 matter upon which the crabs feed, or that they frequent the 

 water of streams into which the crabs may go, but, whether 

 their presence in the branchial chambers of their hosts is 

 accidental or not, '' they would appear to have thriven there, 

 and it is suggested as at least a possibility that they derived 

 sustenance from the blood of the crabs, their chitinous 

 'jaws' enabling them to pujicture the epithelium of the 

 gills or of the vascular lining of the chamber'^ (p. 380). 



Mr. F. W. Edwards has kindly invited me to examine 

 these larvje discovered by Baylis, in order that, by com- 

 parison with other Dipterous larvae, their true systematic 

 position might be determined, and an explanation found, if 

 possible, for their presence in the gill-chambers of their 

 hosts. The results of my investigation are embodied in this 

 communication. 



i\Ir. Edwards sent me two tubes of material, the contents 

 of which, for convenience in the following descriptions, I 

 shall designate by the letters A and B respectively. The 

 first tube contained larvae from the branchial chambers of 

 Cardiosoma hirtipes (Admiralty Islands), while the second 

 tube contained a single larva from Gecarcoidea Icdandii 

 (Christmas Island). 



Desa'iption of Larva A, from the Branchial Chambers 

 of Cardiosoma hirtipes. 



The tube contained two small and two large larvae, all 

 being already in the third stage of development. In each 

 ca^^e the body is very elongate, and furnished posteriorly 

 with a long respiratory siphon. The large larvae (figs. 1 

 and 2), with completely tvaginated siphons, attain a length 

 of 19 to 22 mm., while their diameter at the widest part is 

 only 0*7 to 1 mm. In common M-ith other Cyclorhaphous 

 Diptera, the body comprises a small head, three thoracic, 

 and eight abdominal segments. The head,orj!;5ewf/oce/>7ic/o??, 

 resembles in structure that of all the larvse of tlie Cyclorhapha 

 (fig. 3) ; it is a small, soft, bilobed segment which can be 

 retracted into the thorax, and is furnished with four pairs 

 of sensory organs : [a) the bell-shajied anteniKB ; (U) maxil- 

 lary palps, composed of several small papilla? ; (c) special 

 sensory organs, similar to those previou^^ly described by me 



