306 



PSYCHE. 



[ July— September 1885. 



the last ling. The former arc very 

 small and appear either as points, 

 knobs or fissnres, or Die anterior ends 

 of the tracheae are liiddc-n entirely in 

 a cylindrical invagination of the skin 

 (^Gastrophilits^. The posterior breath- 

 ing-organs are either brealliing-tiibes 

 which are protrusile and retractile 

 (new-born Gastrophilus [p. 36] larvae 

 and Cefhenomyia larvae), or large 

 stigmatal plates which are constrncted 

 according to two kinds of types. One 

 of these types is represented in Gastro- 

 philus and Dcrmatobia, the other in 

 the rest of the genera. The stigmatal 

 plates are more or less protected by 

 lip-like organs on the last ring or by 

 withdrawal into the preceding ring, 

 and are in this way cleaned from sub- 

 stances which adhere to them. 



I have described in detail under that 

 genus the structure of the posterior 

 stigmatal plates in Gastrophilus. The 

 majority of the genera possess how- 

 ever two stigmatal plates in a real sense, 

 consisting of corneous chitinous sub- 

 stance on tiie last ring. Each ring is 

 usually crescent-shaped or reniform. in 

 younger larvae even quite circular, and 

 appears when magnified either as lat- 

 ticed with coarse meshes, finely porous 

 or almost smooth, sometimes radially 

 furrowed. On the inner border of each 

 plate is in all larvae in the third and 

 in many in the second stage a thinner, 

 membranous or knob-like place super- 

 posed or imbedded, sometimes enclosed 

 in the plate itself. The attachment of 

 the trachea corresponds to this place on 

 the inside. Since it usually lias the 



appearance of an opening, and also has 

 been taken for sucli, I call it the false 

 stigmatal opening. It has not vet been 

 ascertained without doubt tiiat breath- 

 ing goes on in such stigmatal plates, but 

 it probably takes place through pores of 

 the plate. It seems to me as if the 

 plates were penetrable especially at the 

 circumference of the attaciiment of the 

 tracheae. 



3. The new-born larvae all possess 

 external mouth-parts ; in tlie later 

 stages lai-vae with oral hooks and those 

 without them are to be distinguished. 

 An internal pharyngeal framework of 

 various development always occurs ; 

 this encloses the membranous gullet 

 and by its muscular structure is of es- 

 sential service in the sucking of the 

 larva. If oral hooks are present, they 

 are connected with this by a joint. 



Usually a U-shaped, bent chitinous 

 plate is to be seen, whose open side 

 looks upward ; from the side it lias the 

 shape of a sitting butterfly whose large 

 upper wing reaches far back and has 

 the smaller, narrow under wing under 

 it. Since the wings of tlie two sides 

 are grown together firmly underneath, 

 the whole pharyngeal framew<jrk ap- 

 pears like a flying insect, when the 

 wings are bent apart from above, and 

 with the base in a plane. The part 

 lying more or less in front, which is to 

 be found in tlic middle between the 

 wings, and which really radiates out 

 into these, or is united with tiiem like a 

 ligament, is what Schroeder van der 

 Kolk calls the tongue-bone. 



In the pliaryngeal framework there- 



