Microscopical Essays. 35? 



magnifier, and in a favourable light, appear twifted like a fmall 

 •cord. The mufcular fibres of the fpider, which are much larger 

 than thofe of the caterpillar, are found on examination to confift 

 of two fubflances, one foft, and the other hard ; the Iafi is twilled 

 round the former fpirally, and thus gives to it the afore-mentioned 

 eord L like appearance. 



If the mufcles are feparated by means of very fine needles, in a 

 drop of fome fluid, we find that they are not only compofed of 

 fibres, membranes, and aerial veflels, but alfo of nerves ; and 

 from the drops of oil that may be feen floating on the fluid, that 

 they are alfo furnifhed with many uncluous particles* 



The number of mufcles in a caterpillar is very great, exceeding- 

 by much thofe of the human body ; the reader may form fome 

 idea of their quantity, by looking at Fig. 1* and 2, 3 and 4, of 

 Plate XII. They occupy the greater!; part of the head ; there is 

 an aftonilhing number at the oefophagus, the interlines, &c. the 

 fkin is as it were lined by different beds of them, placed one un- 

 der the other, and ranged with very great fy.mmetry. 



The number of mufcles that our obferver has been able to 

 diflinguifh is truly aflonifliing ; he found 228 in the head, 1647 m 

 the body, 2066 in the inteftinal tube, making in all 404 1„. 



The spinal marrow, and the brain of the- caterpillar, if 

 they can be faid to have any, feems to have very little relation to 

 thofe of man ; in the laft, the brain is inclofed in a bony cavity : 

 it occupies the greater! part of the head, and is anfractuous, and' 

 divided into lobes. There is nothing iimilar to this in the cater- 

 f*?, • " >i]£j -pillar;.. 



