OF THE STATE ENTOMOLOGIST. 85 



riddle of his existence — when I recall the fact that he has likewise 

 remained undiscovered by eastern observers, and that the males of 

 closely allied European species are unknown — the impression becomes 

 irrisistible that these insects are metagenetic, and that, just as in the 

 closely allied plant-lice, {Aphidce)^ they may and do go on multiplying 

 agamically for a series of generations, and that the male only occa- 

 sionally appears. To strengthen the impression, M. Signoret informs 

 me that M. Balbiani absolutely denies that the presence of the male 

 is necessary in the Leoanides^ a subfamily of larger bark-lice. It 

 would also seem that in accordance with what appears to be a very 

 general law both among plants and animals,* the male is in some 

 way connected with weakened vitality; for with the very batch of 

 leaves and twigs from which I bred the 6*, came the statement that 

 the insects seemed to be dying out, and were less injurious ; and, cer- 

 tain it is, that wherever I have found the male scales on the twigs, it 

 was always on such as were so thickly covered with the other scales, 

 that these were two or three thick and many of them aborted. More- 

 over, it is well-known that this bark-louse has, during the past few 

 years, become less and less troublesome in portions of the North-west- 

 ern States, which suflfered so much from its injuries ten and fifteen 

 years ago. It seems to have lost vitality, and in carefully examining 

 some trees in the vicinity of Dubuque, Iowa, I had no difficulty, last 

 August, in discovering a certain percentage of male scales. However, 

 the question as to whether our Oyster-shell Bark-louse can multiply 

 agamically, or not, is easily settled by a few simple experiments, 

 which will doubtless be made by those who have the proper opportu- 

 nities. Even believing, as I do, in agamic multiplication in this case, 

 we may, nevertheless, naturally conclude, from analogy, that there is 

 a limit to it, and that without occasional fecundation, eggs would 

 eventually either become addled, or the female die without giving 

 birth to them; and on this hypothesis we can account for the abortive 

 scales which are often found without any trace of the contents having 

 been destroyed by other agencies. 



MODE OF SPREADING. 



Having already (Rep. 1, p. 15) referred to this subject, I allude to 

 it again only because a good deal of wonder has been expressed at 

 the wide extent of this insect's range, considering that it is active but 

 three or four days in the course of the year. Dr. LeBaron records 

 some interesting observations, which show that the active larvas are 

 seldom blown by the wind more than three rods from the outermost 

 branches of a tree, and he thinks that the theories so far propounded 



*SeeRep.4, p. 65; also an article " On the Relation between Organic Vigor and Sex, " by [Dr. 

 Henry Hartsiiorne, read before the Am. Ass. for Adv. of Science, at Dubuque, and partly copied in 

 the American Naturalist for December, 1872; also Gardeners' Monthly, November, ISli, 'and [Old and 

 New, February, 1S7'2. 



