'228 



KNOWLEDGE 



[December 1, 1891. 



draws it back through the fore end of the head ; at last it 

 stands still, with the point of the head firmly abutted 

 against the skin." While the animal was in this position 

 he seized it gently with forceps, and endeavoured to detach 

 it from the skin, hoping thus to see the extended proboscis. 

 But in this ho was disappointed, for though a slight 

 resistance to his efforts was experienced, showing that the 

 proboscis had really penetrated the skin, yet- when the 

 insect was detached, no trace of a proboscis, or anything of 

 the sort, could be seen ; it had instantly shot back into the 

 head, and returned to the normal position of rest. This 

 method therefore having proved ineffectual, the experi- 

 menter decided for a time to confine his observations to 

 the upper surface of the insect during theprogressof its meal, 

 so as to watch, through the transparent skin, the gradual 

 drinking in of the blood. Allowing it therefore to attach 

 itself once more, he sees "at the top of the head, under 

 the transparent sldn, between and a little in advance of 

 the eyes, a triangular blood-red point appear, which is in 

 continual movement, expan- 

 sion and contraction alternating 

 with increased rapidity. Soon 

 this pulsation becomes so rapid 

 that several contractions may 

 becoimtedinasecond." Swam- 

 raerdam also had noticed this, 

 and likened the rapid move- 

 ments of this little pumping 

 machine to the quick oscillation 

 of the balance-wheel of a watch . 

 Schiodte continues, " the whole 

 digestive tube is now in the 

 most lively peristaltic move- 

 ment, filling itself rapidly with 

 blood, as is easily observed ; the 

 long (esophagus is particularly 

 agitating, throwing itself from 

 one side to another inside tlie 

 neck, bending itself so violently 

 as to remind one of the coiling 

 of a rope when being shipped 

 on deck." 



The insect was now thoroughly 

 hard at work, and this was 

 therefore the opportunity for 

 the next stage in the pro- 

 ceedings. In order to prevent 

 C C^ "V~--S'T— df- the retraction of the proboscis 

 II \ \ which would have followed the 



I / /-~-\ \ \ withdrawal of the insect, the 



experimenter determined to de- 

 capitate it suddenly, hoping 

 that thereby the proboscis 

 might remain extruded. The 

 fore part of the insect was 

 therefore rapidly severed with 

 a i)air of fine scissors without 

 previously disturbing it in its 

 feast. The decapitated head, 

 having been left as it was for a short time, was then 

 gently raised with forceps, and the proboscis gradually 

 withdrawn ; the whole was then transferred to a slip of 

 glass and placed under the microscope without pressure. 

 The appearance presented was such as is shown in the 

 accompanying diagram (Fig. 2). A long fleshy tube was 

 depending from the mouth, at its base was a stouter part 

 furnished at its apex with a number of hooks, but the rest 

 of the tube was thin, flexible and transparent. Within 

 the latter could be traced four thin chitLnous bands, the 



Fig. 2. — Probo; 

 Louse. (Afb 



representatives of the two pairs of jaws, the mandibles 

 and masillffi of the ordinary insect's mouth. Thus we 

 have an arrangement resembling in some degree that of 

 the mouth of the bed-bug and other Hemiptera, a tubular 

 labium containiug four setiB, the mandibles and maxilhe. 

 During the prjcess of the extrusion of this apparatus 

 the first part to appaar is the strong base of the tubular 

 labium, but the hooks are at first inside the tube. They 

 can, however, be everted, and by a continuance of the 

 same process the membranous lining of the tube is 

 brought out and forms the long delicate sucker which 

 constitutes the greater part of the proboscis. The labium 

 having been inserted into the skin, say through a sweat 

 pore, the hooks become everted and hold the proboscis 

 steady by clinging to the tissues around. The piercing 

 mandibles are then thrust out ; towards their tip they 

 are united into a tube from within which the second pair 

 of setffi is protruded, similarly united, and terminating in 

 four small lobes, which seem to act as feelers. All this 

 mechanism can be tiirust out to varying distances, and 

 hence the length of the exserted proboscis can be accom- 

 modated to the thickness of the skin of the victim in the 

 particular plice in which the animal is feeding ; by this 

 means the capillaries of the host are at length reached, 

 when blood will at once ascend the proboscis, the flow 

 being accelerated and continued by the vigorous action 

 of the pump-like cavity in the digestive tube already 

 mentioned. 



But to return to our decapitated head. The observer, 

 wishing to examine the structure of the proboscis under 

 a higher power of the microscope, put it under pressure 

 for that purpose, when instantly the whole apparatus 

 shot back into the head, and no further observations 

 could be conducted ; in this position the two sides of 

 a chitinous band marked a in the diagram look some- 

 thing like biting jaws, and had been mistaken for such 

 by those who had not seen the protruded instrument. 

 These appear as a dark band across the under surface of 

 the head in Fig. 1, which was drawn from a specimen 

 prepared for the microscope, and therefore more trans- 

 parent than usual, and beneath them the outlines of the 

 retracted proboscis can be traced. Schiodte had to carry 

 out many other observations on specimens prepared in a 

 variety of ways before the whole of the details enumerated 

 above could be determined, and whoever wishes to verify 

 these results must be prepared to exercise great patience 

 in the investigation. Leeuwenhoek was so much struck 

 with the beauty and delicacy of this feeding apparatus, 

 even so far as it was known in his time, that he appeals to 

 its complex character as evidence that a creature which 

 possesses so elaborate a sucking pump could not have 

 been, as was formerly believed to be the case, spontaneously 

 generated from "dirt, sweat, or excrements," but must 

 have an origin similar to that of more highly organized 

 animals. 



('/'» //(• rdntiliiU'il.) 



Hcttcts. 



[The Editor does not hold himself responsible for the opinions or 

 statements of correspondents.] 



To the Editor of Knowledge. 



Dear Sir, — I beg to enclose for insertion in your paper 



what I claim to be a fresh discovery in figures, should you 



think it worthy of your notice. How to tell by inspection 



whether a number is or is not a perfect square or a perfect 



