180 F. X. WILLIAMS 



A larva quite near hatching shows the gland in the process of 

 collapsing and of sinking into the body cavity. A freshly hatched 

 larva, i.e., one a day old, has already lost the first abdominal 

 appendages, remnants of which can be found in the body cavity. 

 (According to Patten the pleuropods in Acillus are absorbed, 

 while in the June-beetle, Melolontha vulgaris, they are probably 

 pushed off (Graber). In other cases they seem to be in part 

 cast off and in part absorbed). The gland-cell nuclei are now 

 clearer, show scattered large pieces of chromatin; the cells them- 

 selves are breaking down, and the whole is forming a rather 

 deep U-shaped mass. Large phagocytes occur in the vicinity; 

 the cuticle and unmodified hypodermal cells are present above 

 the organ, so that it is probable that they have spread over and 

 covered the void made by the retracted gland-cells. 



The pleuropod of Photinus is somewhat different morphologi- 

 cally from that of Photuris. It is more convex and elongate, 

 the cells form a convex instead of a later, flat disc, their nuclei 

 are distal, and correlated with this is the apparently internal 

 basal secretion instead of the largely distal one as occurs in the 

 pleuropod of Photuris. A conspicuous receptacle of non-glandu- 

 lar cells, E, calling to mind the cup of an acorn, surrounds and 

 constitutes the basal portion of the pleuropod. 



The remaining abdominal segments in either genus bear very 

 small and inconspicuous appendages. 



Korschelt ('12) describes and figures in several stages, the 

 pleuropodia of Dytiscus marginalis. Evidently their develop- 

 ment and their degeneration much resemble that in Photuris, 

 in that they at first bear some resemblance to a thoracic leg, 

 later become somewhat mushroom-shaped, with longer nuclei 

 and a glandular character, and finally cave in and sink into the 

 body shortly before eclosion. Korschelt refers to the pleuro- 

 podia as 'Drusenorgane.' 



The pleuropods were first noticed by Rathke, in 1844, in the 

 mole cricket, Gryllotalpa. They do not appear to be of general 

 occurrence among hexapod embryos. They are here (as in the 

 Orthoptera and some Hemiptera) much larger than the follow- 

 ing abdominal appendages. Many transitional forms occur. In 



