Januaby 1, 1890.] 



KNOWLEDGE 



41 



\^ AN ILLUSTRATED "^^ 



MAGAZINE OF SCIENCE 



SIMPLY WORDED— EXACTLY DESCRIBED 



LONDON: JANUARY 1, 1890. 



CONTENTS. 



The Common Flea. — II. By K. A. Butler 41 



The Life-History of a Fern. By E. Mansel Svmpson, 



M.A., M.B. Cantab 43 



Some Properties of Numbers. By Robt. W. D. Christie 45 



Growth and Decay of Mind. By the late R. A . Proctor ... 47 



Tortoises and Turtles. By R. Ltdekker, B.A. Cantab. ... 48 



Harvard College Observatory. By A. C. Ranyard ... 51 



Notices of Books 52 



Letters :—W. T. Lynn, B. J. Hopkins 55 



The Face of the Sky fop January. By Herbert 



Sadler, F.R.A.S. ... ... ... ... ... ... 55 



Whist Column. By W. MoNTAGn Gattie 56 



Chess Column. By W. Montagu Gattie 57 



THE COMMON FLEA. -II. 



By E. A. Butler. 



THE digestive apparatus of a flea (Fig. 4) consists of 

 parts very similar in their arrangement and func- 

 tion to those of tlie cockroach, and tlierefore needs 

 no detailed de.scription. The a'sophagus is a 

 rather short and narrow tube leading into a tliick- 

 walled gizzard, which, again, opens by its broader end into 

 a capacious bag, the stomach, big enough to hold a large 

 draught of blood, such as the insect is only too eager to 

 suck in whenever it can get the opportunity. At the jtmc- 

 tion of the stomach with the intestine are four long, thin, 

 blind tubes, the Malpighian tubules. The hinder end of 

 the intestine expands into an inverted pear-shaped cavity, 

 the rectum, on the walls of which are six oval glands. 



The alimentary canal, when gorged with blood, can be 

 rapidly emptied by the insect, and its contents ejected with 

 considerable force, when a new and good supply of food 

 presents itself before the last meal is disposed of. The 

 dark stains on linen, that indicate where fleas have been, 

 consist of their dried excrement, and are composed of the 

 undigested remains of the blood corpuscles contained in 

 the food. Judging from the fact that rooms that have 

 long been unoccupied are sometimes found to be swarming 

 with fleas, it would seem that the perfect insects ciin sub- 

 sist for a time without their customary food, although 

 they are rapacious and insatiable enough when it is 

 obtainable. And even under ordinary circumstances their 



* Tlio phitc illustrating this papoi- ha.s been uiailo from photo- 

 graphic onlargemonts of a iiiale and female flea pi-epared for the 

 magic lantern by Messrs. Frederic Xewton & Co., Opticians, of No. 3, 

 Fleet Street, E.G. 



living must not unfrequently be precarious, and their 

 meals most irregular. As is well known, it is not every 

 human being that they regard as tit to supply them with 

 nutriment ; some individuals they seem instinctively to 

 avoid, whether by reason of a greater thickness and tough- 

 ness of skin, or of something distasteful in the blood, or 

 from some other cause, it is impossilde to say. That they 

 should prefer a host with a 

 soft and delicate skin is only 

 natural, and is endenced by 

 their marked partiality for 

 females and yoimg children, 

 though it must not be for- 

 gotten that some of this 

 apparent partiaUty may be 

 due to the extra facilities 

 that are afforded to the 

 parasites, in the case of 

 these sections of the com- 

 munity, by the character of 

 the clothing, the greater 

 looseness of which renders 

 them easier subjects for the 

 fleas to gain access to and 

 therefore to operate upon. 



In consequence of the 

 compression of the body 

 and the comjsarative trans- 

 parency of the sldn, many 

 details of internal anatomy 

 may be made out in the 

 living flea, if it be examined 

 under the microscope ^\•ith 

 ^Jf' *■— PiGESTivE Apparatus g^^^i ilhumuation bv trans- 

 OF Dogs Flea. ce, ajsophaens; •... j i- i . mi / i 

 .,, gizzard: .,, stom;ch ; ,„ mal- mitted light. The trache.e, 

 pighian tubules; ;, intestine; i; or breathing tubes. Can thus 

 rectum. (After Landois.) be Very easily traced, even 



down to many of their 

 finer branches, and the large trunks that traverse the 

 length of the body are especially conspicuous objects ; 

 large branches may also be easily seen running down the 

 legs. If the flea is confined so that it can only move 

 sUghtly, the contraction of the muscles, especially in the 

 coxie, can be watcheil without any difficulty, as any little 

 twitchings occur in the legs. A Uving flea is a very pretty 

 object when viewed with polarised light. 



The original photographs from wliich the enlargements 

 in the accompanying plate were taken were obtained fi-oiu 

 specimens prepared for the microscope, and therefore 

 completely flattened. In the process of mounting, the 

 thoracic segments unavoidably become slightly dislocated 

 from their natural position ; this is especially noticeable 

 in the male. The greater part of the contents of the 

 body also have been dissolved out, in order to increase 

 the transparency of the object, and hence very little of 

 the internal anatomy can, in these specimens, be seen. 

 The most prominent object in this connection is the 

 reproductive apparatus of the male ; the bars and coiled 

 threads at the hinder extremity are all parts of these 

 organs, and are really internal in position, though they 

 hardly seem so. The coiled threads are attached to 

 the part of the organ that can be protruded. 



We have now to trace the life history of the flea. The 

 eggs are oval, whitish, sticky things, and though, of course, 

 actually minute, are yet rather large in proportion to the 

 size of the insect itself, their longest diameter being about 

 ^th of an inch, and the shortest ^Vr'-''- '^o f*'" '^^ '■'"^ 

 human species is concerned, the eggs appear to be laid, 

 not upon the body or clothes of the host, but amongst 



