272 CONTRIBUTIONS TO THE NATURAL HISTORY 



Far from consisting exclusively of short ovate cells connected together in several rows, 

 we have here very thin threads, in which the cellular appearance is almost entirely gone, 

 excepting where they combine to form a plexus, in which some of the threads have the 

 appearance of long caudate cells. For a time I mistook these threads for muscular 

 fibres ; but they differ from muscular fibres quite as much as they do from the main 

 nervous cord. They are somewhat peculiar in their appearance in every respect, and 

 from their connection with the chymiferous tubes, from the disposition of their plexuses 

 and the circular connection between them, and from their connection with the sen- 

 sitive bulbs below, I have been led to consider them as parts of the nervous sys- 

 tem. What corroborates this view is, that I have never noticed any indication of 

 contractions in these fibres, although contractions are so readily observed in the real 

 muscular cells ; while, on the other hand, the plexuses which they form remind us rather 

 of the arrangement of nervous fibres than that of muscular fibres ; so that, though some 

 doubt may be entertained as to the real nature of this system, it seems more natural to 

 consider the whole of these threads as nerves than as any thing else. I am the more disposed 

 to consider them so, since, in Sarsia, a similar system has been traced having similar con- 

 nection with the surrounding parts, bearing, perhaps, still less resemblance to the muscular 

 system ; and though I have spoken of it with some hesitation, I trust that further investiga- 

 tions will confirm this view. The fact that some threads arising from the plexuses below 

 the arch of the chymiferous tubes descend along the sides of the main central digestive 

 cavity, might be further considered as another indication of the-nature of this apparatus; 

 for muscular fibres could perform no function in connection with this cavity ; the less so, 

 as the whole cavity, as such, is capable of extensive contractions and dilatations by 

 means of its own tissue, as described above. Finally, there is one circumstance agreeing 

 with this view, which ought not to be overlooked, namely, that isolated threads arise 

 from the middle of the threads extending from one plexus to another, and descend verti- 

 cally from this circle along the main vertical inner bundles of muscles. 



Thus the analogy between this apparatus and what has been observed in Sarsia is so 

 complete, as to afford another argument in favor of the view I have taken of it in this 

 animal. If this view is correct, the nervous system of Hippocrene, like that of Sarsia, 

 would consist, 1st, of a main circular cord round the lower margin, following the circular 

 chymiferous tube ; 2d, of vertical threads following the vertical chymiferous tubes ; and 3d, 

 of a circle above, around the central digestive cavity, but at some distance from it. The 

 main distinctive peculiarity between this system and that of Sarsia would consist in the 

 plexuses below the arches of the radiating tube, which have not been noticed in Sarsia. 

 This sensitive system is observed to be in so close connection with the sensitive buds, as 



