426 TEGUMENTARY ORGANS 



the vertebrate classes. Thus in Argulus foliaceus the peripheral 

 nerves become pale, and divide, and at the point of division there is 

 a ' nucleus ' as in the embryonic fibres of the frog. In Artemia salina, 

 Branchipiis stagnalis, and in the Heteropod Mollusk Carinaria, the 

 termination of the tegumentary nerves is essentially similar. The 

 larva of the Dipterous insect Corethra, presents even peculiar sensory 

 appendages, in the delicate plumed hairs which beset the sides of the 

 body. These are articulated in the ordinary way, and have an 

 internal ligament, a sort of spring, attached to their base, which is 

 enlarged and receives the enlarged and cellaeform termination of a 

 nervous twig. It will be obvious that this arrangement is peculiarly 

 fitted for communicating the slightest vibration to the nerves. 



In the Vertebrata (fishes, reptiles, man), the ordinary mode of 

 termination of the integumentary nerves is in one or two plexuses, 

 whence the fine terminal branches proceed, and end by dividing into 

 minute branches indistinguishable from the imperfect elastic fibrils 

 of the enderonic tissue. Loops have also been observed, but it is 

 impossible to say whether, in any case, these are real terminations or 

 not. Gerber and Kolliker have also described " nerve coils " in 

 animals, and in the conjunctiva and lips of man. 



The simplest form of sensory appendage in the Vertebrata is 

 presented by the large papillse of fishes, into which a bundle of nerve 

 fibres enters, some of which terminate in the papilla, while others, 

 whose looped bands may be readily distinguished, probably pass out 

 again. 



In certain fresh-water fishes (Barbus, Leuciscus), Leydig has 

 described papilla; of this kind, which have a cup-shaped depression at 

 their extremities, lodging a globular mass of what he describes as 

 modified epithelium. 



Special modifications of the tissue of the papillae for sensory 

 purposes in the fingers, tongue, lips, &c. of man have lately been dis- 

 covered by Meissner and Wagner, and described by them, under the 

 denomination of the Corpuscula tactih. Kolliker, who doubts their 

 special relation to the tactile function, on the other hand, prefers to 

 call these bodies, axile corpuscles. They are simply ovoid masses of 

 imperfect connective tissue occupying the centre of the papilla:, and 

 further distinguished by having their endoplasts and imperfect elastic 

 fibrils arranged transversely to the axis of the papilla, so that they 

 appear to be made up of transverse superimposed laminte {^fig. 320). 

 One or two dark-contoured nerve tubules come up through the base 

 of the papilla, and running along one side of the corpuscles, thin out and 

 terminate, without, so far as I have been able to see, entering its substance. 



