OF WASHINGTON. 309 



tents of the sac into the nest of pointed blades. At the same time an 

 egress is afforded the liberated spermatozoa through the mouth of the 

 duct the only point not constricted by the radiating fibres and once 

 within its walls a successive contraction of its muscular fibres, like the 

 vermicular action in the small intestines of mammals, would cause their 

 ready descent to the oviduct. Thus the spicules not only serve to liberate 

 the spermatozoa, but also to facilitate their egress through the attached 

 base, where the spermatophore wall is thinnest. 



2. PSEUDO-CENCHRI. 



A feature which in Pronuba synthetica tends to add to its saw- 

 fly resemblances is a pair of cenchri-like spots on the metathorax 

 which are transversely ovoid and more or less iridescent and trans 

 lucent, showing the more distinctly by their pale color as com 

 pared with the darker piceous coloring of the thorax itself. In 

 denuding a number of specimens in other families of Lepidoptera 

 to see how general these cenchri-like spots are, I have been led 

 to some rather interesting observations.. I find that they are 

 noticeable in other species of the Tineina, but are easily over 

 looked because the vestiture generally hides them, and further 

 because they are not ordinarily as specialized as in Pronuba. 

 They are superficial and yet with a sufficiently differentiated struc 

 ture to be quite noticeable, the surface being covered with trans 

 parent papillae which easily rub off. The true cenchri of Hy- 

 menoptera seem to be little understood by writers, and, in fact, 

 they have received comparatively little study as to their function. 

 They vary in structure in the different families, so far as the few 

 observations I have made justify a conclusion, but generally con 

 sist of a scale which forms a sort of lid to a cavity protected by a 

 membrane and which indicates that they may be organs of sound 

 rather than of any other sense. They occur on the metathorax 

 immediately behind the scutellum in Tenthredinidae and Uroceri- 

 dae, and are generally referred to as light-colored spots, or more 

 minutely as by Andre as " two small symmetrical callosities, 

 usually light and semi-transparent; rarely they are covered, as in 

 Lyda, by a sort of scale or overlapping hood, and their function 

 is not known." They are called granulae by Thompson, and 

 cenchri by most others. 



A closer examination of their structure shows that they are 

 always or very generally in the form of scales, which are free on 

 the posterior end and side, and thus form a hood or projection 

 over an opening into the body cavity. This opening, so far as 

 can be determined in dried specimens, is protected by a delicate 

 membrane. 



The scale-like protection of the cenchri, as described from the 

 species of Lyda, is inaccurate, for the scale is the cenchrus, which 



