272 Mr. J. W. Dunning on the 



though published only in 1878, is dated " December, 1875 ;" 

 it contains the result of the author's experiments from 

 1870 — 75 and no later ; so that my prediction of 1876 

 was no prediction at all, as Ritsema had in fact done in 

 1875 the very thing which, in ignorance of his observations 

 of that year, I had prophesied he would do. 



The following is a short recapitulation of Ritsema's 

 experiences (Tijd, v. Ent. xxi. pp. 81 — 92) : — 



On the 14th June, 1870, he first captured the insect 

 (a dozen, all males), at a fish-pond called Kolkje, not far 

 from the village of Overween, near Haarlem, where it had 

 been previously found by Weyenbergh. On that occasion 

 he searched in vain for larva3, but a fortnight later he 

 found, on Potamogeton crispits, in the angle of the leaves 

 against the stem, some white silken cocoons which con- 

 tained the empty skin of a pupa, having on each side three 

 ])rominent stigmata. On the 14th July, he found in 

 similar webs some unhatched pupae ; and on the same day 

 a full-groAvn larva which was busy spinning up. In 

 August he collected more larv», which, however, differed 

 considerably in size ; he placed them in an aquarium on 

 P. crispus, and they remained in the larva state throughout 

 the winter. 



At the end of March and in April, 1871, he collected 

 more larvse, and placed them with the others. At the 

 end of April some of them began to spin, whilst others 

 had not attained half their growth. But about the middle 

 of May, Kitsema went from home, and on his return, 

 plants, larvas and pupte were all dead. He had, however, 

 sent a full-grown larva to Heer Brants, which, in the latter 

 half of June, produced a female moth, furnished with rudi- 

 mentary wings ; and this was all that resulted in the season 

 of 1871. 



On the 12th May, 1872, Ritsema went again to the 

 Kolkje, and found not only larvje and pups in sufficient 

 numbers, but specimens also of the male imago. Several 

 male moths having previously emerged from the pupa?, 

 on the evening of the 26th May a female was observed 

 moving quietly over the Potamogeton, under water; this 

 also had only rudimentary wings. On the next day 

 Ritsema left home, and on his return there was a repe- 

 tition of the catastrophe of the previous year — plants, 

 larvffi and pupfe were all dead ; there were, hoAvever, in 

 the aquarium several dead moths, all males but one, and 

 the one female possessed only rudimentary wings. 



