[65]

20th Morning R. Cabbage

Red Cabbage

Black 6. 55 7 40 from light to light 8°   8' 28   same spot 9. 15   almost in same spot 9. 35   from light 10 20   from light 11   same course from light

Red 6 55.   first move to window 7°. 40 obliquely to light to light  8°   8° 28   move to light 9. 15   a little from light 9. 35   same course } 10. 20   to light & right 11° to light & left zig-zag 1 3/8 inch

from glass to tip of Bristle 13 4/8

Distance of tip of Bristle & mark 1 1/8

glass to mark 14 5/8

Nutation of Cots & stems in darkness of rather old seedlings   (2)

glass 13 4/8 inch 14 5/8— [sketch] 1 1/8 mark multiplies 13 times.

(Used)

(Used)

Nutation of Cots & stems (2) in darkness of rather old seedlings

[65v]

81 93

Chap. 8

gall-making Cecidomyiiæ (Diptera). With some common species of Saw-flies (Tenthredinæ) Mr. F. Smith has reared hundreds of specimens from larvæ of all sizes, but has never reared a single male: On the other hand Curtis says 68*(DD) that with same kinds of saw-flies certain species (Athalia) which he bred by him the males to the females were as six to one female; whilst exactly the reverse occurred with specimens the mature insects of the same species caught in the fields. With the Neuroptera, Mr. Walsh states that in many, but by no means in all, the species of the Odonatous groups (Ephemerina), there is a great overplus of males: and again that generally in the genus Hetærina, also, the males are generally at least four times as numerous as the females. In certain groups of species in the genus Gomphus the males are equally numerous, whilst in two other allied species the females are twice or thrice as numerous as the males. In some European species og Psocus thousands of females may be collected without a single male, whilst with other species of the same genus both sexes are common 69*(EE). In England Mr. McLachlan has captured hundreds of the female Apatania muliebris, but has never seen the male; and of Boreus hyemalis only four or five males have been here seen. 70*(FF). With most of these species there is no reason to suppose that the numerous

[Descent 1: 314: "n all the gall-making Cynipidæ known to Mr. Walsh, the females are four or five times as numerous as the males; and so it is, as he informs me, with the gall-making Cecidomyiiæ (Diptera). With some common species of Saw-flies (Tenthredinæ) Mr. F. Smith has reared hundreds of specimens from larvæ of all sizes, but has never reared a single male: on the other hand Curtis says,68 that with certain species (Athalia), bred by him, the males to the females were as six to one; whilst exactly the reverse occurred with the mature insects of the same species caught in the fields. With the Neuroptera, Mr. Walsh states that in many, but by no means in all, the species of the Odonatous groups (Ephemerina), there is a great overplus of males: in the genus Hetærina, also, the males are generally at least four times as numerous as the females. In certain species in the genus Gomphus the males are equally numerous, whilst in two other species, the females are twice or thrice as numerous as the males. In some European species of Psocus thousands of females may be collected without a single male, whilst with other species of the same genus both sexes are common.69 In England, Mr. MacLachlan has captured hundreds of the female Apatania muliebris, but has never seen the male; and of Boreus hyemalis only four or five males have been here seen.70 With most of these species (excepting, as I have heard, with the Tenthredinæ) there is no reason to suppose that the females are subject to parthenogenesis; and thus we see how ignorant we are on the causes of the apparent discrepancy in the proportional numbers of the two sexes.
68 'Farm Insects,' p. 45-46.
69 'Observations on N. American Neuroptera,' by H. Hagen and B. D. Walsh, 'Proc. Ent. Soc. Philadelphia,' Oct. 1863, p. 168, 223, 239.
70 'Proc. Ent. Soc. London,' Feb. 17, 1868."]