1888.] MICROSCOPICAL JOURNAL. 229 



regarded by the best autholities as an aberrant family of Diptera^ or two- 

 winged flies. I should remind you here that the word Aptera means wing- 

 less, while the word Diptera means two-winged. Though fleas do not now 

 possess wings, you will see that naturalists have placed them among the two- 

 winged insects, because in classification more attention has been recently 

 paid to the life-histories of organisms, and to the genetic affinities which exist 

 between them, than was given to these matters before it was seen that unsus- 

 pected relationships subsist between creatures which in adult life appear to 

 difter materially from each other. 



To resume my description of the larva of the flea, each segment of its body 

 is beset with long hairs ; Packard tells us there are four to each segment. 

 The head has a horny scale or shield on each side and bears two three-jointed 

 antennse, which are very unlike the antenuEe of the mature flea. The terminal 

 segment ends in two curved spines, which probably aid the larva in moving 

 forward. You will find drawings of all these parts in my sketch-book. The 

 larva I had under observation fed on the pellets of congealed blood which, 

 as I said, were deposited with the eggs. Packard aflfirms that the larvae of 

 the cat-flea live on decaying vegetable substances — a not unimportant fact, 

 perhaps, in its bearing on the history of fleas. The larvae of the dog-flea 

 reared by me were supplied with no food besides blood pellets ; but though 

 I never caught them at it, I sometimes suspected that they practised gross 

 cannibalism on the sly ; certainly their numbers thinned without any apparent 

 cause, and as they lay at the bottom of a covered finger-glass, up the steep 

 sides of which they could not climb, it is difficult to account for their dis- 

 appearance. 



On the 25th October, the seventh day after they left the egg-case, I found 

 them curling up and edging off' from the masses of dried blood; and sup- 

 posing they might be about to moult or to pupate, I placed a small fragment 

 oi piittoo in the finger-glass as a kind of hospital comfort. Eyeless though 

 they were, the larvae quickly swarmed into it, and there thev spun little white 

 silken cocoons. In my note for the 35th October, 1SS6, I find this record : — 

 'The writer in Science -Gossip had a difficulty in rearing his larvte, and 

 lost them when they were fit for the pupa stage. It is clear he missed this 

 necessary addition to their comforts.' In m}' own case several larv£e were 

 already dead when I placed the puttoo in the glass. A more recent observer 

 writing to the same useful little journal. Science -Gossips recommends flea 

 larvte being placed on woollen cloth when about to pupate, so that what I 

 did before he published his observations is evidently the correct thing. The 

 pupa were visible in most of the cocoons and were decidedly flea-like in form ; 

 the}' looked like rough wax life-size models of fleas, with enough of the 

 mummy thrown in to convince one they were still pupie. On Tuesday, 

 November 3, 1886, most of them quitted their cocoons as perfect, active fleas. 

 My brood were, therefore, in the egg for, say, 50 hours, larvae for six days, 

 and pupie for eight days ; in other words, they completed their metamorphoses 

 in a trifle over sixteen days, attaining their adult state on the 17th day after 

 the eggs were deposited. Westwood, cited by Packard, savs fleas are larvEe 

 for twelve days, and that the period of pupation varies from eleven to sixteen 

 days. Westwood also seems to consider that they may even hibernate in 

 the larval state. It is quite possible that the periods vary in different climates, 

 perhaps even at different periods of the year. There obviously are marked 

 differences between the periods given by Westwood and those observed by 

 me in Calcutta ; but as I watched- the brood closely, and recorded all my notes 

 at the time of observation, I think what I have said ma}' be accepted as 

 correct for Calcutta at the season at which I worked. 



A few remarks in closing as to the significance, from a wider point of view, 

 of tliese and similar insect transformations. W^hat, briefl}'. is their import.^ 



