Microscopical Essays. 



223 



%ith a cruftaceous habit, more than it does that of naked worms 

 or caterpillars ; it is moderately hard, and like the rough fkin called 

 fhagreen, being thick fet with a number of grains, evenly diftri- 

 buted. The fubftance of the fkin is firm and hard, and yet very 

 flexible. 



On each fide of the body are nine fpiracula, or holes, for the 

 purpofe of refpiration j there are no fuch holes vifible on the 

 tail ring a, nor on the third ring counting from the head ; for at 

 the extremity of the tail there is an opening for the admiffion and 

 expulfion of air : in the third ring the fpiracula are very fmall, 

 and appear only under the fkin, near the place where the embryo 

 wings of the future fly are concealed. It is remarkable that cater- 

 pillars, in general, have two rings without thefe fpiracula; per- 

 haps, becaufe they change into flies with four wings ; whereas, 

 this worm produces a fly that has only two. 



The fkin has three different {hades of colour; it is adorned with 

 oblong black furrows, with fpots of a light colour, and orbicular 

 rings, from which there generally fprings a hair, as in the figure 

 before us, only the hair that grows on the infe&'s fide is repre- 

 fented ; befides this there are here and there fome other larger 

 hairs c e. The difference of colour in this worm arifes from the 

 quantity of grains in the fame fpace ; for in proportion as there 

 is a greater or leffer quantity of thefe, the furrows and rings are 

 of a deeper or paler colour. 



The head d is divided into three parts, and covered with a 

 fkin, the grains on which are hardly difcernible. The eyes are 

 rather protuberant, and lie forwards near the fnout. It has alfo^ 



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