78 Tachinidae. 



and haemorrhoidalis, and in the latter stalked) are deposited in 

 summer on the hairs, especially on the fore legs and fore part of the 

 horse, but haemorrhoidalis deposites on and at the lips and nasalis 

 on the underside of the head. The eggs hatch and the small larva 

 gets free ; it is now eitlier licked ofT or it fmds itself its way to the 

 mouth. The opinion is also advanced that it bores in under the 

 dermis and that the horse, because of the tickling, should scratch 

 with its teeth and thus get the larva into its mouth. When in the 

 mouth the larva perhaps also here bores in (see f. inst. Hadwen and 

 Cameron: Bull. of Ent. Research, IX, 1918, 91, with literature). 

 However it now may be the larvæ later on, in autumn or winter, get 

 down into the stomach, where they sit, often in very large numbers 

 (100 — 200, sometimes even up to 1000) with their heads in the 

 mucosa; here they hibernate and quit the host with the excrements 

 in June and July; they then go into the ground and pupate, and 

 the fly emerges after four to six weeks. 



Young larvæ of Gastrophilus have sometimes been found on 

 man, especially on children, below the dermis, where they then, 

 as they wander forwards, form an undulated red line: "creeping 

 disease"; also from Denmark a case has been recorded, but especially 

 from Russia. The larva does not develop, but the case is in so far 

 interesting, as it points towards the possibility mentioned above 

 that also on the normal host the larva goes through the dermis. 



Of the genus eight European species are known; four occur in 

 Denmark. The three of our species now occur in North America, 

 but are here originally introduced, and no special American species 

 is known. 



Table of Species. 



1. Wings without posterior cross- vein 1. fecorwn. 



■ — Wings with posterior cross-vein 2. 



2. Wings with a dark transverse band and a spot at apex; 

 hind trochanters in male with a large triangular pro- 

 longation, in female with a smaller one; hind femora 

 suddenly thin at base 2. equi. 



— Wings without markings; trochanters and hind femora 



simple 3. 



3. Posterior cross-vein considerahly behind medial cross- 

 vein 3. haemorrhoidalis, 



— Posterior cross-vein a little before or just below medial 

 cross-vein 4. nasalis. 



