1224 Dr Gairdner's Analysis of 



circle, which encircles the oesophagus of the mollusca, except 

 that in this case the whole circle is situate on the dorsal or up* 

 per side of that canal. From the point of contact of this ner- 

 vous circle with the dorsal vessel, it gives off two very slender 

 twigs forward to the anterior part of the head, where, in other 

 forms of the Rotatoria, such as the Rotifer vulgaris, the two 

 red points (eyes) are situate. In some, such as the Eosphora 

 najas, a single large red point is situate on the back of the 

 neck, in the exact position of the ganglion at the apex of the 

 circle *. The above mentioned large mesial oesophageal gan- 

 glion (brain) sends off posteriorly another branch of much larger 

 size, backwards along the abdominal surface of the animal, 

 which closely adheres to the internal layer of its double enve- 

 lope. 



That these different filaments and gangha, to which we have 

 given the name of nerves, are not muscles, is evident from their 

 form, their mode of insertion into the integuments, and because 

 in the contractions of the animal they are not shortened, but 

 assume a serpentine form, being apparently quite passive. They 

 are not vessels, because no pulsation nor motion of a contained 

 fluid has been hitherto perceived through their transparent tis- 

 sues. If they are not organs of an entirely unknown nature, 

 the whole analogy of their form and position, compared with that 

 of the nervous system in other invertebrate animals, favours the 

 idea of this being their true nature. 



We may here consider as appendages to the nervous system, 

 those coloured points situate in the anterior part of the head 

 of these animals, and most usually on the dorsal surface, which 

 have been considered as eyes. As already noticed, the first 

 discovery of these organs was made in 1816 by Nitsch, who saw 

 in the Cercaria viridis (now referred by Dr Ehrenberg to the 

 o-enus Euglena) three black scaliform points. In the Rotifer 

 vulgaris, their pigment is of a red colour, and they are three in 

 number, two small ones at its anterior extremity, and a single 

 larger one at the nucha in the situation of the apex of the 



• The best view of the disposition and appearances of the oesophageal 

 ganglia, is got from the dorsal side of the animal, in a line with the great 

 dorsal vessal. The nervous collar given off from the brain, is however best 

 s6en on a lateral view. 



