577 



gill-nerves and Ramus lateralis, and then describes how in the Labrax 

 lupns the R. infestinalis vagi forms near the division of the Arteria 

 coeliaca into Art. hepatodnodenale and Art. mesentero-spleniale, a 

 strong Plexns coebacus with the N. splanchnieus, which originates 

 from the first al)dominal sympathetic ganglion. No such plexns is 

 mentioned by Chevrkl in the case of Cyprinoids. As the latter 

 resembles Labrax in the main, there is no reason to assume that 

 though not mentioned it should not be fourd here. The probability 

 that the branch innervating the esophagus receives sympathetic fibres 

 by means of the splanchnieus is therefore very gieat, and becomes 

 practically a certainty if sympathetic fibres can be identified in the 

 thinnest nerve-ramifications on the muscular fibres. 



We know that in the striated muscle three kinds of nerve-endings 

 may be met with. First the epilemmal sensible nerve-endings, secondly 

 the hypolemmal endings connected with nerve-fibres possessing a 

 myelin sheath, the so-called motoric endplates of Kühnk, thirdly, 

 much more delicately shnped networks, always originating, as far 

 as we know, from the marrowlcss fibres, which are called accessory 

 endplates. BoEKir describing this sjtecies takes them to be endings of 

 sympathetic fibres. 



From DK Bokr's publications we have known for a few years 

 that the sympathetic fibres maintain the tonus of the muscles. 



The presence of accessory endplates in the sphincter ductus pneu- 

 matici has rendered in my opinion the antagonistic innervation vei'y 

 probable. 



For the study of the motoric endplates I used the silver-impreg- 

 nation of BiEiscHOWSKY as prescribed by Bokke. The results, obtained 

 for the present by this method, are made clear in fig. 'J — 3. 

 Histological particulars conceining the course of the nerve-fibres and 

 the shape of the endplates may be omitted here. The main ])oint 

 is that in the muscle closing (he esophagus and ductus motoric end 

 plates of 2 kinds may be met with. 



The hypolemmal nerve-fibrils without a medullary sheath as far 

 as they could be traced, were thinner than those with one. The 

 endplates were less marked and mostly ended in simple loops. 



Hence there are good reasons for assuming that the sphincter is 

 innervated in two ways, that the stimulation of the tiervus sympathi- 

 cus keeps up the tonus, and that of the vagus removes it. 



The easiest w-ay of investigating the function of the ductus sphinc- 

 ter is to expose tlie fish to a modified air-pressure. 



