352 Microscopical Essays. 



pillar ; we find indeed in the head of that which we are defcri- 

 bing, a part which feems to anfwer the purpofe of the brain, be- 

 caufe the nerves that are difleminated through the head are 

 derived from it ; but then this part is unprotected, and fo fmall, 

 that it does not occupy one- fifth part of the head ; the furface is 

 fmooth, and has neither lobes nor any anfra&uoftty : and if we 

 muft call this a brain, the caterpillar may be faid to have thirteen, 

 as there are twelve more fuch parts following each other in a line; 

 they are nearly of the fame fize with that in the head, and of the 

 fame fubftance, and it is from them that the nerves are diflributed 

 through the whole <body. Left the idea of thirteen brains might 

 be difagreeable to his readers, M. Lyonet has called thele parts 

 ganglions. 



The fpinal marrow in the human fpecies defeends down the 

 back, inclofed in a bony cafe ; is large with refpeft to it's length, 

 and not divided into branches, diminilhing in thicknefs in pro- 

 portion as it is removed further from the brain. In the caterpillar, 

 the fpinal marrow goes along the belly, is not inclofed in any 

 tube, is very fmall, forks out at intervals, and is nearly of the 

 fame thicknefs throughout, except at the ganglions. For a de- 

 fcription of the innumerable vefiels, and curious texture of thefe 

 parts, we muft refer the reader to M. Lyonet's work. The fub- 

 ftance of the fpinal marrow, and of the ganglions, is not near fo 

 tender and eafily feparated as in man ; it has a very great degree 

 of tenacity, and does not break without confiderable tenfion. The 

 fubftance of the ganglions differs from that of the fpinal marrow, 

 as no vefiels can be di [covered in the latter, whereas the former 

 are full of very' delicate ones. The patient anatomift of the 

 , 'caterpillar has counted forty-five pair of nerves, and two fingle 

 a ones ; 



