470 Miscellaneous. 



peculiar swellings perform the function of organs of touch ; but it is 

 impossible to find any relations between the cells which compose 

 them and nervous elements." 1 have been able to detect both the 

 nerves and their terminations, and this both by means of serial sec- 

 tions and by observations on the living animal. 



The different kinds of pedicellariaD — gemmiform, buccal, tridact3'le, 

 and trifoliate — are to be regarded as exquisite sense-organs. But 

 besides this function of sense-organs, they possess the most various 

 other functions, according to their form, size and structure, and 

 their arrangement upon the test, and these may be ascertained by 

 experimental investigations and by careful observation of the mode 

 of life. The investigation of the minute structure must go hand in 

 hand with these. 



If we examine the inner surface of the three jaw-pieces of Stron- 

 gylocentrotus lividus, we observe in tbe base of each jaw-piece a 

 tumuliform convexity, which is covered with rigid seta?. These 

 elevations are sense-organs, which consist chiefly of epithelial sense- 

 cells, as I have already found to be the case and described in Aste- 

 rida and Holothuriae. At their free ends these cells bear tactile 

 setae, while their basal portions are continued into the finest fibrils, 

 which ramify and are connected with the nervous plexus. A branch 

 nerve runs to each tactile elevation, branching off from a larger 

 nerve-stem, which may be traced to the apex of each valve. 



I have found the following statements to apply universally to all 

 the various forms of pedicellaria; as regards the ramification and 

 course of the nerves. In the head of each pedicellaria three nerve- 

 stems are distinguishable, running in the interstitia of the three 

 adductors of the valves. Each nerve-stem runs to the apex of the 

 valve in a direct lino. Throughout its course branch nerves of 

 various strength are given off on all sides, which pass to the sense- 

 organs, the musculature, and the glandular sacs. In the iuterstitiu 

 of the three muscular bundles (adductors) there issue very fine fibrils 

 intermixed with ganglion-cells, producing a network of nervous 

 threads which enter the musculature. 



In Echinus acutus there are two tactile elevations {pedicell. cjem- 

 miformes) on the inside of each valve. One of these is basal, the 

 other is placed just below the hooked calcareous tip. Between 

 these we find a third sense-organ of simple structure, situated about 

 in the centre of the inner surface of the valve. Between these 

 organs sense-cells are scattered through the whole epithelium, as is 

 shown by the nerve-threads passing to them. 



In Strongylocentrotns lividus there is only one tactile elevation on 

 the inner surface of each valve ( pedicell, gemmi formes) ; it is placed 

 basally, while the apex of the valve is covered with sense-cells. 



In SphcerecMniis gramdaris the sense-organs are limited to three 

 elevations, situated basally on the inner surface, and these again 

 show separate projections upon which tactile sctoe arise. These 

 projections are composed of cells, which form an organ reminding 

 one of the gustatory papilliB of the higher animals. These struc- 

 tures are composed of both sense- and supporting cells. 



As regards the course of the nerve-stem, the so-called tridactyle 



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