204 M. E. Haase on Abdominal 



third pair of legs of the Iulidae must be referred to the abdo- 

 men. 



As to the Pauropoda, they can only be regarded as rami- 

 fications of the great Protodiplopodan stem, degenerated by 

 a subterranean mode of life, among other things the tracheal 

 system having been completely lost, but which also in their 

 genitalia and development still show throughout the funda- 

 mental form of this type, represented in a minor degree by 

 Polyccenus, whilst their buccal organs and antennas are 

 aborted. 



The examples of polypodism in the embryos of insects cited 

 at the commencement had in common the comparatively long 

 •persistence of the rudiments of the first pair of abdominal legs, 

 and recent investigations have even shown that, before their 

 final disappearance, these may undergo special transforma- 

 tions. As long since as 1844 Ratlike had observed peculiar 

 " pilzhutartige Korper," also afterwards detected by Korot- 

 neff and V. Graber, and regarded them as " branchiform 

 respiratory arrangements." Ayers also subsequently disco- 

 vered on the same segment of the embryos of (Ecanthus 

 lateral excrescences of the ectoderm, which he described as 

 vesicular appendages, united with the body by a short 

 peduncle and lined with a layer of large cells, the cavities of 

 which were connected with that of the body, and which he 

 characterized as " branchiae." 



Further, in Blatta, W. Patten described the transforma- 

 tion of the leg-appendages of the first abdominal segment into 

 similar " pear-shaped structures," but urged against their 

 interpretation as branchiae their thick cell-lining, and ascribed 

 to them rather a sensorial function and a glandular one to their 

 lining. The author has found similar appendages also on 

 the first abdominal segment of tolerably mature embryos of 

 Periplaneta orientalis. 



While in Hydrophilus, according to V. Graber, the appen- 

 dages of the first abdominal segment persist in the rudimentary 

 state, on the embryo of the Cockchafer they show, according 

 to the same naturalist, a considerable increase in size. As 

 early as the seventeenth day * they have become compara- 

 tively stronger in growth than the typical legs, while " the 

 originally very inconsiderable rudiments of the other (abdo- 

 minal) segmental appendages have entirely disappeared " — 

 nay, they finally become much longer than the thoracic legs 

 and almost three times as broad. They then form a soft sac 

 which is united with the body by a short peduncle, lined 

 with large ectodermal cells and filled internally with meso- 

 * Morphol. Jahrb. xiii. (1888) p. 599. 



