1. Attempts have been made to modify the sex in various species of Tenthredinidæ by immersing leaves holding saw-fly eggs in chemical solutions during maturation which occurs during the first three hours after egg-laying.

2. In Pristiphorapallipes, Lep., which in England appears almost completely thelytokous, it is possible that sex-change has occurred as the result of such treatment for, in five experiments, eggs up to one and a half hours old treated for one hour in a 0.2 per cent, solution of magnesium sulphate (in distilled water) yielded 62 females, 2 males, and 1 intersexlike specimen.

3. Definitive interpretation of these appearances cannot be made until more experimental results are obtained, and more is known of the sex-ratio of the species.

The breeding experiments of the writer and Miss E. F. Chawner, in England, involving the rearing of some 600 specimens during eight successive parthenogenetic generations show the male percentage to be between 0.5 per cent, and 1.75 per cent. In Canada Garlick finds it to be 2 per cent, fcom 232 individuals of five successive generations and part of the sixth; larvæ from cultivated bushes yielded 207 ♀ ♀ ; wild larvæ from a wild bush gave 4 per cent.--1 ♂ : 23 ♀ ♀. In South Europe Enslin states that the male is not rare.

4. The external characters of these rare English males and the abnormality, and the external genitalia of one male and the abnormality are described in detail.

5. Externally the abnormality shows the slim build of the male, but has certain female colour characters; its external genitalia comprise a male set, complete except for the genital plate, succeeded by a complete female set of which the two halves of the saw-sheath are smaller than normal, modified in shape and wide apart; the saws and saw-guides lie horizontally instead of sagittally; internally there is a spermatheca and paired gonads leading into normal male ducts ; each gonad to appearance resembles a small ovary with about five follicles, but cytologically they are almost empty except for a few indeterminate cells, a few nurse-cells, and relatively few spermatozoa.

6. This specimen may be either (a) a gynandromorph which genetically is a male with teratological gonads and possessing somatically certain substitutive female characters and arr additive female segment interpolated posteriorly; or (b) a gynandromorph genetically a male with teratological gonads and somatically a female with an additive male genitalring interpolated posteriorly; or (c) an intersex predominantly male (cf. moth intersexes of Goldschmidt, Harrison, and others).

7. Non-disjunction in either a male (X) or female (XX) pallipes egg during segmentation--and preferably during the later stages--could produce the condition of the abnormality.

8. The prime cause to non-disjunction in this almost completely thelytokous species cannot be abnormal intra- or inter-specific fertilisation, but may be hereditary or pathological--both unlikely--or physical or/and chemical disturbance in the relationship between the egg and its nidus in the leaf. Of the latter a possible natural cause is the occasional imperfect deposition of an egg so that a portion of it is exposed to the outer air, but the more likely explanation is the artificial experimental treatment.

9. The simultaneous appearance of two of the extremely rare English males and a unique abnormality from eggs treated as mentioned under (2) strengthen the possibility that these results were artificially produced. It is quite possible that the gonads of the abnormality were not intersexual but teratological, the chemical affecting the germ-tissue in shape only but not in sex.

10. Eight other sexual abnormalites in saw-flies, from other workers' records, are briefly described in their externals principally ; it is tentatively suggested that in the light of recent research they may be classified into two categories, (a) gynandromorphs, (b) intersexes; two of these specimens, Nematinus umbrinus, Zadd., taken wild, may be intersexes resultant upon an inter-specific cross umbrinus x ribesi

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