152 Proceedings of the Royal Physieal Society. 



the granular matter inside ttie setae consists of " nerve- 

 granules." He does not seem to have experimented at all 

 on their function, and for him all setse are tactile. 



Leydig, in 1860,^ besides describing the so-called olfactory 

 setae, mainly in Daphnidae and Phyllopods, says, talking 

 especially of the antennules of Asellus, " besides those hairs 

 which have the nature of simple outgrowths of the integu- 

 ment, and stand with their root over a cuticular canal, where, 

 through a continuation of the matrix, one might say a papilla 

 rises towards the hair," these " possess also ' Tastborsten,' 

 i.e., simple pointed or feathered hairs, which at their base are 

 connected with a nerve- ending." He gives, however, no 

 account of the minute structure or distribution of the seta3, 

 or of the structure of the nerve-ending, nor do his figures 

 give us any assistance. In his " Lehrbuch der Histologie " 

 (Fig. 113), he shows the connection between nerve and setae 

 in the larva of Borethrct 'plujiiicornis, but to this we shall 

 return later. 



Hensen, in his admirable paper,^ touches upon the relations 

 of the auditory setae to others, and to him also is due the 

 credit of establishing the exact nature of the connection 

 between nerve and seta ix\ the auditory setae. 



Dr W. C. M'Intosh ^ gives a very elaborate account of the 

 variations of the setae in that species, but his researches are 

 made purely from the standpoint of a microscopist, and he 

 has no uniform standard, but each seta is described by itself 

 without any attempt at generalisation. 



Sars,* in describing Mysis oculata, var. relicta, considers 

 that touch is localised in the antennae, and says that the 

 setae have a structure which seems to endow them with great 

 sensitiveness ; they are very thin and fine, with contours 

 clear at first, then tapering suddenly; they are irregularly 

 grouped all over the stem, with a large number on the last 



^ Ueber Gelior = und Geruclisorgane der Krebse und Insekten, Miiller's 

 Archiv, 1860. 



^ Ueber das Geliororgan der Decapoden, Zeitschr. -fiir "Wissench. Zoolog. xiii. , 

 1864. 



^ The Hairs of Carcinus mcenas, Trans. Linn. Soc, 1863. 



^ Histoire naturelle des Crustac^s d'eau douce de Norvege Christiania, 

 1867, p. 38. 



