1884. 



129 



eggs yielded 5 living and 3 dead $ flies ; a single insect perished in 

 the larva stage. All the cocoons had been kept through the winter 

 under similar conditions in metal boxes in a drawer. Of the 4 doubly 

 parthenogenetic flies only one laid a few eggs which did not develop. 

 Besides the 6 male flies, the lot of 270 yielded also at least 4 $ flies, 

 w^hich showed one of the (^ characteristics to a greater or less extent, 

 that is, the basal ring of the abdomen, in place of being quite light 

 as in the $ , w^as much darker in various degrees, almost to perfect 

 black. But none had the masculine lateral tufts at the apex of the 

 abdomen. The males, when put with females for the purpose of 

 breeding, seem invariably to suffer mutilation in the loss of their tarsal 

 joints, especially of the fore feet, in their struggles with the female. 

 In union, the attitude observed was venter to venter. 



Whether, then, it is to be attributed to continued parthenogenesis 

 or to the effect of prolonged artificial and unfavourable conditions of 

 life, the changes observed appear to be threefold : Jirsf, there is a 

 smaller number of flies excluded alive from the cocoons, thus — in the 

 282, 270 and 32, respectively came out 1 in 2, 1 in 2.7, and 1 in 8 ; 

 whilst in the case of the 9 cocoons from fertilized eggs, more than 

 half excluded living flies, and in all but one of the remainder the 

 insects had reached the imago state : secondly/, there is progressive 

 infertility ; flies from fresh larvse lay eggs abundantly, their de- 

 scendants much more sparingly, and in the third generation hardly 

 any eggs were produced : thirdly, we see a striking increase in the 

 proportion of males in the second generation. 



That so many insects should perish in the cocoon points perhaps 

 to the effect of unfavourable artificial conditions. The diminution in 

 fertility might also be referred to weakening of the constitution from 

 the same cause ; but the increase in the number of males in the second 

 generation, and the increased viability in the 9 cocoons from fertilized 

 eggs, seem to indicate a necessity for recurrence occasionally to 

 sexual reproduction. It is curious that in the case of bees, &c., the 

 exactly converse necessity prevails ; without a mixture of agamic re- 

 production the species would become extinct. On the theory of Yon 

 Siebold, &c., fertilized eggs of bees would yield no males in the next 

 generation, and a generation of virgins would produce nothing but 

 drones, with which the community would come to an end in the 

 grandchildren. 



J 



3 



rtilii 



Milford, Letterkenny : 



October, 1884. 



