XO. 6 GRASSHOPPER ABDOMEN SNODGRASS 37 



tapering or rounded at the ends, and having sharply defined margins 

 formed by the covering cuticula (fig. i6 C, /). These structures are 

 the so-called " rectal glands." In the grasshopper there is nothing to 

 suggest that they have a secretory function, the surface cuticula being 

 relatively thick, and the epithelium, as shown by Tietz (1923). con- 

 sisting of simple columnar cells. For the same reasons, also, it does 

 not seem probable that the rectal pads are organs for the absorption 

 of water from the faeces (see Wigglesworth. 1932) ; in fact, any 

 other part of the rectum would appear to be better adapted to an 

 absorptive function. On the other hand, the hard flat surfaces of the 

 pads, forming six plaques in strong relief on the inner wall of the 

 rectum, suggest that, by contraction of the surrounding circular mus- 

 cles, the structures may serve to compress the contents of the rectal 

 sac and thus extract water from the faeces. 



V. THE OVIPOSITOR AND ASSOCIATED STRUCTURES 



The ovipositor of the x\crididae is primarily a digging organ that 

 works by a forcible separation of the short recurved valvulae. It thus 

 dififers radically in its action from the usual egg-laying organ of other 

 insects, in which the valvulae are interlocked and move lengthwise 

 on one another. The acridid ovipositor, therefore, has quite a dififer- 

 ent mechanism from that of the sliding type of ovipositor. Though 

 the prongs of the grasshopper's ovipositor, as shown by their develop- 

 ment, are without doubt homologues of the valvulae of other insects. 

 it is apparent that the usual supporting basal plates, or valvifers, are 

 absent, and that the musculature of the acridid organ has little relation 

 to that of an ovipositor in which the muscles of the valvifers are the 

 principal motor elements. A second important function of the acridid 

 ovipositor, however, is that of manipulating the eggs, as the latter 

 issue from the oviducal opening, in such a manner that they may be 

 placed appropriately in the egg cavity for the exit of the young 

 grasshoppers. 



STRUCTURE OF THE OVIPOSITOR 



The exposed part of tlie grasshopper's ovipositor consists of a lower 

 and an upper pair of strong, sclerotic, pronglike processes with curved 

 tips turned ventrally and dorsally (fig. i, Ovp). These processes 

 are respectively the first and third valvulae (fig. 17 A, iVl, 3VI). 

 The second valvulae {2VI) are small, and are ordinarily concealed 

 between the others, but they are not rudimentary in the sense of being 

 functionless structures. The ovipositor projects posteriorly at the 



