12 



FIFTH REPORT OF THE ENTOMOLOGICAL COMMISSION. 



proved in an extensive and beautifully illustrated memoir* the fact 

 of alternation of generations in a number of European species. 



In a notice of Adler's work in the American Naturalist for July, 

 1881, Professor Riley added that Mr. H. F. Bassett "has, following 

 Adler's interesting experiments in Europe, suggested the probable di- 

 morphic connection of several of our vernal galls which produce bisexual 

 individuals, with autumnal forms which produce larger asexual flies. 

 Dr. Adler gives a list of nineteen species of Cynipidte in which the oc- 

 currence of dimorphic forms has been proved, giving the names of 

 the agamic forms and the corresponding bisexual forms the latter 

 of which, in all cases, were referred to distinct genera by previous ob- 

 servers. 



In this connection should be mentioned the remarkable fact that in 

 certain closely allied species {Aphilotrix seminationis, marginalis, quad- 

 rilineatus and albopunctatus) no alternation of generations seems to 

 occur. 



Saw-flies. — These often seriously injure evergreen trees, while they 

 occur on all other trees. There are a large number of species. Their 

 larvae resemble caterpillars in appearance and in voracity. The flies dif- 

 fer from wasps, etc., in the abdomen being broad at the base; the body 

 is somewhat flattened, and the head is wide, while the antennae are not 

 elbowed, and as in Lophyrus are pectinated in the males, serrated in the 

 females. In the end of the hind body of the female is situated the 

 "saw" or ovipositor. This consists of two blades, the lower edge of 

 the lower one of which is toothed like a saw, and fits in a groove in the 

 under side of the upper blade; both blades being protected by sheath- 



Fig. 1.— Saw of a saw-fly (Hylotoma) : a, lateral scale ; i, saw ; /, gorget. After Lacaze-Duthiers. 



like stylets. On pressing the end of the abdomen the saw is depressed ; 

 by this movement the saw, which both cuts and pierces, makes a gash 

 in the soft part of the leaf, where it deposits its eggs. (Fig. 1.) 



The Lophyrus of the pine makes a series of punctures on each side of 

 a pine needle ; the Nematus of the alder makes from twenty to forty pairs 

 of semicircular punctures in the under side of the midrib of the leaf, 

 while the larch saw-fly inserts her eggs in two alternating rows at the 



*Zeit8chrift lur Wissenschaftliche Zoologie, sxxv, Feb. 1, 1881, pp. l.')l-246, Pis. 

 X — xii. Dr. Adler's researches were commenced in 1875, and his first paper appeared 

 in 1877. (Deutsche Entomolog. Zeitschrift, 1877, Heft 1.) 



