128 



[November, 



two were males, which is curious, and if the disparity be real is sug- 

 gestive of polygamy. In former years I have often beaten this tree 

 without any result ; the present occurrence of this Idiocerus seems, 

 so far, to confirm Kirschbaum's remark concerning it — "Auf Populus 

 alba und caiiescens stellenweise haufig." Failing the opportunity to 

 draw up a description, Mr. Edwards has had the goodness to do so 

 from some of my captures. — J. W. D.]. 



A POSTSCRIPT CONCERNING- PARTHENOQENESIS IN ZAR^A 



F ASCI AT A. 



BY J. A. OSBORNE, M.D. 



The observations made by me this year on Z.fasciata may have 

 some interest as bearing on the questions of parthenogenesis and sex. 

 Last year (1883) I had 310 cocoons made by larvse that had been 

 taken off the bushes the year before. Of these about 28 were ich- 

 neumonized, and from the remaining 282 (or thereabouts) 142 living 

 flies (of which only one was a (5*) were excluded during the summer. 

 On opening the other cocoons I found dead larvse, nymphs and flies, 

 in 31 of which the sex (?) was determinable, making 172 females in 

 all to one male. In the present year the results have been somewhat 

 different. I had a stock of 311 cocoons classified as follows: 270 

 were w'hat I may call singly parthenogenetic, i. e., reared from par- 

 thenogenetic eggs laid by flies emerging from cocoons spun the yeai 

 before by larvse taken from the bushes ; 32 were doubly partheno 

 genetic, i. e., bred from unfertilized flies, themselves parthenogeneti 

 cally bred from larvse taken in 1881. These and their parents 

 therefore, had been in captivity and under artificial conditions som< 

 three years. The third lot consisted of 9 cocoons reared from egg 

 laid after observed union between the ^ and $ . From the 270 cocooni 

 only 100 living flies were excluded, and of these 3 w^ere males. D 

 the remaining 170 cocoons, besides 134 dead larv^ and 1 mould: 

 nymph, I found 32 dead ? and 3 c? flies ; that is, no less than Q ^t 

 129 ? flies, or a proportion of 1 : 21.5 ; or, if we add to these 12 

 $ flies, 23 more from the other two lots, making a total of 152, th 

 proportion of (^ to ? flies is still only low^ered to 1 : 25.3 as agains; 

 1 : 172 in those flies bred from free larvse and only one year in coii 

 finement. 



From the 32 doubly parthenogenetic cocoons only 4 living fli( 

 were excluded, all ? , and in the unopened cocoons I found, besid« 

 dead larvse, 11 more ? flies. The 9 cocoons from presumably fertilize' 





