2G6 SPECIAL HISTOLOGY. 



scribed free terminations of the nerve fibrils, and their inser- 

 tion with expanded ends into the muscular fibres, as Doyere 

 in the Tardigruda, and Quatrefages in Eolidina, and some 

 Rotifera ('Ann. d. Sc. N./ 1843, p. 300, and pi. 11, fig. 12). I 

 myself, in a larva of Chironomus (a dipterous insect), noticed a 

 single nerve-fibre, proceeding to the two muscular fasciculi of 

 the simple tarsus, bifurcate into two branches, which were 

 implanted upon the surface of the muscle, with somewhat 

 expanded terminations. In the Vertebrata, Muller and Briicke 

 first described division of the nerves in the orbital muscles of 

 the Pike (J. Muller, ' Physiol.,' 4th ed. vol. 1, p. 524), and in 

 Amphioxus, Quatrefages noticed conditions precisely like those 

 met with in the Invertebrata above mentioned. The observa- 

 tion is easily confirmed, as respects the orbital muscles of the 

 Pike, in which, upon the teasing out of the fasciculus either of 

 the fresh muscle as well as after it has been treated with 

 corrosive sublimate, and rendered transparent by acetic acid, 

 numerous divisions of the nerves are apparent. They are 

 nevertheless not nearly so frequent in this case, as in the Frog, 

 nor are the divisions more than bifid or trifid. Besides this, 

 1 was especially struck with the glaring contrast that was 

 presented, to what is seen in the Mammalia, in the enormous 

 extent of space included in the distribution of the nerve-fibres ; 

 a distribution so extensive, that it is by no means easy to find 

 a single primitive fasciculus which has not a nerve-fibre going 

 to it ; in many places even, the latter were seen in apposition 

 with a fasciculus throughout a great extent, and surrounding 

 it with loops, or with a variable number of spiral convolutions. 

 A similar condition was observed by R. Wagner in the orbital 

 muscles of the Torpedo, whilst in other muscles the nerves were 

 very scantily supplied (' Gott. Nach./ Oct. 1851). In the Am- 

 phibia, divisions and free terminations of the nerves have been 

 described by Wagner. The former are remarkably beautiful 

 and numerous. They commence in nerve-fibres, measuring 

 0-004 — O^OOG"', in the smaller trunks and branches, and are 

 several times repeated, with a gradual diminution of the fibres, 

 until extremely minute filaments measuring 0"001 — 0-0015'" 

 are formed. The divisions are for the most part di- or tri- 

 chotomous, more rarely multiple ; in one instance, however, 

 Wagner noticed eight ramusculi. The ultimate filaments are 



