"218 PSTCHH. iOctober— December 18S4. 



HEAD OF LARVAL MUvSCA— PRELIMINARY NOTE. 



BY GEORGE MACI.OSKIE. PHINCETON . N. J. 



The tuuscidae are usually said to lKi\e 

 headless lai-vae. The real state of 

 matters however is that their head is 

 buried in their thorax, to be thrust out 

 at will during larva-hood, orpermauent- 

 Iv in the adult. Some years ago I spent 

 fruitless time in attempting to investi- 

 gate this structure ; but recent researcii- 

 es on the head and proboscis of the adult 

 have enabled me to return to the attack 

 with greater success. Mr. Walter M. 

 Rankin has cut for me some excellent 

 transverse sections of the head of the 

 larva o(Miisca caesar, and bv their help 

 as well as bv teasing I have got the 

 following results. 



1. The head has a double skeleton, 

 the one independent of the other : ( 1 ) 

 a large dark-colored case, figured bv 

 Weismann,' consisting of proximal, 

 mid-, and distant parts, the distant part 

 being the well-known "hooks" (really a 

 bifurcated piece) ; (2) a cbitinous arma- 

 ture lining the pharynx : outside of the 

 pharynx-wall (therefore organically in 

 the head) are muscles which join it to 

 the larger, dark-colored case. 



2. The dark-colored part represents 

 the fulcrum, mid-segment, and the fork- 

 ed distal supports of the proboscis of the 

 adult. The relation of parts is the 

 same as in the adult : the salivary duct, 

 made by the union of the ducts of the 

 paired salivary glands, enters the mouth 

 at the mid-proboscis as in the adult. 



' Zeilschr. f. wiss zool., 1S63-1S66. 



and the longitudinal and transverse mus- 

 cles are much as they shall always be. 



3. The '-hooks", or forked distal 

 part, appear to be the precursors of the 

 upper fork of the adult disti-proboscis : 

 they have also inferior processes repre- 

 senting the inferior fork of the same. 

 Perhaps these hooks are the mandibles. 



4. The armature of the pharynx 

 consists of a chitinous sheath lining its 

 lumen. On the floor of this are eight 

 longitudinal i)ars. which are found on 

 cross-section to be hollow, each with a 

 longitudinal slit opening towards the 

 lumen of the pharynx. 



5. On tracing the pharynx-arma- 

 ture to its anterior extremity we find 

 that it terminates al)ruptlv bv a rim 

 which supports a number of teeth at the 

 roots of the longitudinal bars referred 

 to. Here we have evidence that the 

 longitudinal bars of the larva rejjresent 

 the pseudotracheae of the adult ; thev 

 open by a long slit, and ha\e transverse 

 semi-rings so as to produce a resemblance 

 to tracheae, all as in the pseudotracheae. 



6. Hence the slit tubes wliich line 

 the pharynx of the larva are itientical 

 with the pseudotracheae of the adult ; 

 and the swollen '■labella" of the disti- 

 proboscis of the adult are the everted 

 stomodaeum, whilst its supporting forks 

 are probably the mandibles. 



7. The muscular apparatus for open- 

 ing the pharynx is as in the adult. Long 

 muscles descend from the walls of the 



