PABACOROTOOA AKEHMANI (wARREN). 347 



secretory hypodermal epithelium (PL XXI, fig. 92). The 

 gland between VI and VII is especially large {i. g.) Between 

 segments VIII and IX there is a large dorsal, median hypo- 

 dermal gland, with a cuticle-lined receptacle opening to the 

 exterior (PI. XX, fig. 88, and PI. XXI, g. r.) ; it is of similar 

 structure to that of the pair of glands which occur between 

 abdominal tergites V and VI of the imago (PL XVII, fig. 37). 



Associated with the hypodermis there are certain huge 

 secretory cells (PL XX, fig. 89) which possibly assist ecdysis 

 by pouring a secretion under the cuticle. 



Tracheal System. — Not strongly developed. In the 

 thorax there is a fairly large latero-ventrally placed pro- 

 thoracic spiracle, as in the imago ; but no meso- nor meta- 

 thoracic spiracles are present. In the abdomen there are 

 certain minute spiracles which appear to be quite closed by 

 a slightly projecting rod of chitin blocking the end of the 

 tracheal tube (PL XX, fig. 89, sjp.). These spiracles are not 

 lateral, but are placed dorsally, thus foreshadowing their 

 position in the imago. No spiracles could be found on the 

 1st abdominal segment of the larva, but a pair occurs in each 

 of the segments II-VIII. 



The tracheal tubes are embryonic in character and have 

 relatively thick walls composed of peculiarly arranged, 

 flattened cells (PL XX, fig. 89, tr., and PL XXI, fig. 93, 1. 1.). 

 The lumen, when present at all, may be entirely filled with 

 chitin, but occasionally a little air has been detected in it. 

 The relatively coarse tracheal strands branch but little, tmd 

 in the abdomen, at least, can have no respiratory function. 



Nervous System. — As in the case of the imago, the 

 larval brain was studied by means of a model constructed 

 out of pieces of cardboard cut to shape from serial sections. 



The optic ganglion is scarcely distinguishable, but a slight 

 anterior swelling on the outer face of the procerebral lobes 

 doubtless represents it (text-fig. 5, a, op. g.). 



The procerebral lobes bear a marked resemblance in out- 

 line to those of the imago ; there are the same especially 

 flattened lateral sides and steep posterior rounded surface. 



VOL. 4, PART 2. 24 



