Microscopical Essays, 629 



remarkable for it's brightness, may be perceived about the mid- 

 dle of the forehead; many veffels may be feen to take their 

 origin from this. 



The thorax, or breaft, is joined to the head by a fhort annular 

 circle, or neck ; the thorax in fize is nearly one-fixth part of the 

 whole an.malculum. In it we diftinclly perceive the heart of the 

 little creature ; the heart is placed almoft in the middle, the diaf- 

 tole and i) Hole cannot fail to catch the eye of every attentive 

 obferver. it i feen very plainly through the back, {hutting and 

 opening alternately with great regularity and exactnefs. It ap- 

 pears to be compofed of two femilunar parts, wich in the time of 

 contraction approach each other laterally, and form between 

 them a figure fomewhat like a horfe-fhoe, whofe upper fide is 

 flat, the u der one convex. In the diaftole thefe two parts 

 feparate ; the feparation begins exactly in the middle of the lower 

 part next the tail. The alternate motions of the heart are per- 

 formed with great ftrength and vigour. In each of the femilunar 

 parts there is a cavity, which clofes when they come together, 

 and opens when they feparate. 



The motion of the heart is communicated to all the other parts 

 of the thorax, and indeed through the whole animal we may per- 

 ceive contractions and dilatations going on,, that are apparently 

 correfpondent thereto. It is neceflary, however, to remark, 

 that the motion of the heart is fometiraes fufpended, or at leaf! 

 quite imperceptible for two or three minutes, after which it re- 

 commences, and goes on with the fame vigour and regularity as 

 before. From the under part of the thorax a fmall tranfparent 



5 horn 



