WHEELER— AXT LARV^. 3 IB 



diverticula like the embryonic legs, consisting of hypodermis and 

 its overlying cuticula and containing a portion of the fat-body sep- 

 arated from the hypodermis by a granular liquid.^ Now the fat- 

 body of insects may be regarded as a diffuse ductless gland, the cells 

 (trophocytes) of which take certain substances from the blood in 

 which they lie, store them in the cytoplasm as fat-globules or proteid 

 granules and later return them to the blood in a more finely divided, 

 if not chemically modified form. The exudate which accumulates 

 in the distal ends of the exudatoria is therefore merely blood charged 

 with nutrient substances from the fat-cells, and either filters gradu- 

 ally through the hypodermis and overlying cuticle or is forced 

 through them by muscular pressure. At first sight it would seem 

 that the cuticle must be impervious to such a liquid, but a considera- 

 tion of the more recent work on the minute structure of chitin by 

 Holmgren (1901, 1902), Biedermann (1902, 1903), Kapzov (1911), 

 Casper (1913) and others shows that there is nothing to prevent the 

 passage of a thin fatty liquid, even if it were not under pressure 

 and even if the cuticle were much thicker than it is in the ant larva. 

 The cuticle is a colloid, either of a reticular structure, as Kapzov be- 

 lieves, or formed of horizontal layers of very fine fibrillse crossing 

 one another at an angle of 60° as most investigators, including 

 Biedermann and Casper, maintain. Between the fibrillse are regu- 

 larly distributed and extremely fine openings or " pore canals," 

 through which a liquid might readily pass as if the cuticle were a 



^ The question arises as to whether the larval exudatoria of PachysUna 

 are the homologues of the true appendages on the thoracic and first abdominal 

 segments of embryo insects. In other words, do the exudatoria represent 

 true legs or are they new formations? The trophidium of P. latifrons seems 

 to point to the former alternative. The large leg-like exudatoria on the first 

 abdominal segment are certainly very suggestive of the embryonic " pleuro- 

 podia " to which I devoted a paper many years ago (1890). On the other 

 hand, the four pairs of trophidium appendages in latifrons seem to be 

 homologous with the four pairs of papillae in the larva of Bothroponcra 

 (Fig. 4), and the latter are almost certainly merely remnants of a consider- 

 able number of similar papillae which are scattered over the whole surface 

 of the larval Pachycondyla, Diacamvia and Ponera. Furthermore, two of 

 the pairs of exudatoria on the prothorax of the Pachysima ccthiops tro- 

 phidium and the unpaired tentacle-like exudatorium just behind the head 

 cannot be brought into the homology. It would seem, therefore, that the 

 exudatoria must be regarded as coenogenetic, or new formations peculiar to 

 the young larvae of certain Old World genera of Pseudomyrmini. 



