220 



HARDWICKE'S SCIENCE-GOSSIP. 



I have observed the same in several specimens of 

 Pediculus capitis. 



In the specimens examined by myself, the whole 

 of the skin was seen to be reduplicated. Two sets 

 of spiracles, one within the other, were beautifully 

 shown. In all the great tracheal vessels, the spiral 

 membrane was seen to be double, the inner tube 

 being continuous with the outer skin of the abdomen, 

 thus showing that the tracheae are shed as well as 

 the external skin. 



The most interesting fact, however, that my 

 specimens showed, was, that not merely the shell or 

 exoskeleton was about to be shed, but also the 

 muscles that worked the terminal joint, a phenomenon 

 that has not, I believe, been hitherto observed. 



bodies, and are marked with fine transverse striae. 

 The muscle which flexes the outer claw is seen to be 

 entirely outside the inner shell, and must, therefore, 

 be cast off when the animal casts the outer skin. 



It has been objected, by one savant to whom I 

 submitted my specimens and views, that the striated 

 bodies in question are not muscles at all, but merely 

 tracheal dilatations, and that the apparent muscular 

 striation is caused by the spiral thickening within 

 those tracheal dilatations. This objection seems to 

 be frivolous. At any rate, it is easily overcome. If 

 the stria: were due to the tracheal spiral, they would 

 present, when the microscope is focussed half through 

 their substance, a dotted appearance at their ends. 

 This is found not to be the case. 



Fig. 82. — Ecdysis of Pediculus capitis (highly magnified). 



The accompanying diagram, drawn with the aid of 

 a camera lucida, from the foot of a Pediculus capitis, 

 will serve to show what I mean. The last three 

 joints are represented. Within the shell of these can 

 be seen the new skin (/). This is seen to be 

 delicate and wrinkled ; it does not become chitinous 

 until the removal of the outer shell (s). 



The relative position of the two terminal joints, or 

 claws, is peculiar, and has an important bearing upon 

 what follows. It is seen that the terminal claw of 

 the inner, or new limb, lies not within the corre- 

 sponding claw of the outer limb, but within the last 

 joint but one. 



Attached to the base of both of the terminal 

 claws can be seen the muscles—;/",/' — by which they 

 are flexed. They are elongated sub- cylindrical 



The very position of these bodies shows them to be 

 flexor muscles. They are inserted into the only avail- 

 able part of the claws, and lie in the only possible 

 direction in which properly-acting flexors could lie. 



Even supposing that these bodies are not muscular, 

 it stands to sense, from the relative position of the 

 two claws, that the muscles within the inner skin 

 cannot possibly act upon the outer claw. Hence, 

 those that do move the outer claw must lie within 

 the space between the two, and must therefore be 

 thrown off when the ecdysis takes place. 



The specimen from which the drawing was made, 

 was mounted in Canada balsam, after being first 

 treated with potash, and cleared with turpentine. 



James Harvey. 



Scarborough. 



