94 INTERNAL ANATOMY OF INSECTS. 
derer towards each extremity, particularly the anal. In 
some also, as in Aranea domestica, like that of insects, it 
has lateral muscular appendages; but in others, as in 
Clubiona atrox, it is without them*. It exhibits a pair of 
vessels that appear to connect with the gills, by which 
the oxygenation of the blood takes place, and a number 
of others that ramify minutely and are lost in the ana- 
logue of the epiploon, supposed to be their /zver®. Whe- 
ther these last are to be regarded merely as veins, has 
not been ascertained; they seem rather to convey the 
blood outwards, than to return it back to the heart: but 
this question must be left for future investigation. I may 
observe, however, that though the heart of the spider 
has been traced only in the abdomen, it may probably ex- 
tend into the trunk. 
The heart of the scorpion has been examined both by 
Treviranus and Marcel de Serres; but as the descrip- 
tion of the latter is most clear and intelligible, I shall 
principally confine myself to that. The heart, then, of 
these animals is elongated, almost cylindrical, but atte- 
nuated at each end; it is extended from the head to the 
extremity of the tail, and appears to have four pairs of 
lateral muscles. On each side are four pairs of principal 
vessels, which go to the pulmonary pouches, and there 
ramify. These may be assimilated to veins. Besides 
these, there are four other vessels that cross them, form- 
ing with them an acute angle, and which, with four 
branches of smaller size, receive the blood from the pul- 
monary pouches, and distribute it to the different parts 
* Treviranus Arachnid. 28. t. iii. JF. 28, 29: 
» Ibid 29, ¢. iii. f. 30, 31. 
