Dr. G. Meissner on the Genus Mermis. 425 



fibre one way and the other the opposite, becoming lost in the 

 muscular tissue*. 



The histology of this system in animals so minute as these, 

 worked out by an observer so expert and faithful as Meissner, 

 presents mauy note-worthy points. 



The ganglia in question are composed exclusively of ganglion- 

 cells or globules which appear to be the infundibuliform expan- 

 sions of as many nerve fibres that compose the nervous cord con- 

 necting these ganglia with the general system. There are none 

 of the so-called nerve-cells usually found in nervous centres — in 

 fact these central masses rather resemble true ganglionic forma- 

 tions, excepting that they are terminal instead of on the course 

 of a nervous cord. Meissner' s description and figures, especially 

 the latter, are so good, as to leave no doubt that there is 

 here a direct continuity of the nerve-fibre with the ganglionic 

 vesicle. 



In a former notice we alluded to some discrepancy on this 

 point, and as this continuity had been observed by some, and yet 

 not seen by others who had searched carefully for it, we suggested 

 that this direct connection, when present, might be an exceptional 

 condition. But numerous researches since published, and espe- 

 cially the very complete memoir of Axmannf, represent this as a 

 very common disposition of the elements of nervous centres in 

 Man and the Mammalia. The subject is indeed somewhat 

 obscure in a functional point of view, for what is the interpreta- 

 tion of this direct continuity of the vesicular with the tubular 

 portion of this system ? Certainly it is not the essential condition 

 of function between the two, or all nerve-fibres would terminate 

 in this manner, and there would be no ganglionic vesicles but 

 those having this connection. But this, as is well known, is far 

 from being the case. We leave the subject until another time. 

 As to the structure of the peripheric nerves, our author describes 

 them as having at first a distinct fibrillated structure as usual, but 

 that this gradually disappears and the nerve appears as a 

 homogeneous cord. But from our own investigations upon the 

 terminal nerves of some insects, we suspect that this disappear- 

 ance of the true fibrillae may have been apparent and not real ; 

 for we have, in the cases referred to, thought that such was the 

 case, but by using higher powers with some reagents, the fibrillar 

 were seen. We think therefore that whatever may be the mode 



* As Meissner observes, a similar disposition is mentioned by Doyere 

 (Ann. d. Sci. Nat. 1840, xiv. p. 346) in the muscles of the Tardigrada, and 

 by Quatrefages {ibid. 1843, xix. p. 300) in the Eolidina, some Annelides 

 and Rotatoria. 



f Beitr. z. mikroskop. Anat. u. Phys. d. Ganglien-Nerven-systems des 

 Menschen u. d. Wirbelthiere. Berlin, 1853. 



