4^^ Dr, G. Meissner ow the Genus Merniis. 



form ; at least, after we have left the typical forms of the higher 

 animals. Thus, I may mention that Ley dig* found the muscles 

 of the alimentary canal of Artemia among the Crustacea, com- 

 posed of spindle-shaped instead of disk-like elements, so arranged, 

 with the points and bases alternating, as to form a symmetrical 

 fibrilla. In conclusion, we may remark upon this system, that 

 Meissner found no sarcolemma, and no perimysium of the 

 muscular layer. >ia 



Nervous System. — The researches of Dr. Meissner in this 

 direction have particular interest, because the existence of this 

 system in the Gordiacei has been generally denied, and, if seen 

 by previous observers, their statements were most unsatisfactory f. 

 But the histology of this system is quite as interesting. 



Meissner found it so developed that he divides it into three 

 portions: a central, a peripheric, and a splanchnic portion. ul 



The central portion is divided into two parts, one at the ce- 

 phalic, the other at the caudal extremity of the body. In the 

 first are two anterior and two posterior cephalic ganglia, and an 

 CEsophageal ring composed of a superior and an inferior ganglion 

 united by lateral commissures. In the second part, situated in 

 the tail, there are three fusiform ganglia of like character, bwl- 

 smaller than those of the head. da 



The peripheric portion consists of six filaments given off from 

 the upper part of the anterior cephalic ganglia, which go to as 

 many papillae on the head, which are probably organs of sense, 

 — of two lateral cords arising from the superior oesophageal 

 ganglion, which traverse the sides of the body, giving off filaments 

 to the muscles, the skin, &c., and of some smaller twigs from 

 the cephalic centres for the muscles of that region. 



The splanchnic portion consists of two lateral trunks arising 

 from the oesophageal ganglion, which soon meet and unite on 

 the median line of the body, forming one cord which extends to 

 the tail. From this cord are given^pjf filam.eiit^.to the organs 

 of vegetative and reproductive \iiQ> <\qrkhcib yikmrB','' di 



The three cords thus formed, haying traversed the body,- end 

 each in one of the three ganglia above described. We can here 

 allude to only one more point in the disposition of the nervous 

 system ; this is the final termination of the nerve-filament in 

 muscle. According to our author, a twig enters the muscular 

 fibre at right angles to the course of the latter, and upon its 

 entrance divides into two twiglets, one of which runs with the 



* Ueber Artemia salina und Branchipus stagnalis, in Siebold und 

 KoUiker's Zeitsch. iii. p. 280, Taf. 8. fig. 6. 



t Bertliold and Blanchard both supposed they saw cords which might 

 be nerves, but their observations were wholly unsatisfactory ; — for references 

 see Siebold and Stannius' Comp. Anat., Amer. ed., vol. i. § 104. note 5. 



