412 Mr. E. J. Allen. Some Points in the Histology [Apr. 



inner side of the loop a straight arm passes inwards and meets 

 similar arm from the opposite side. A direct fusion of the tsvo 

 has, however, never been observed. 



III. Sensory elements, in which the cell lies outside the gang 

 cord. 



These have been demonstrated bj me up to the present only in 

 abdomen of lobster embryos. The cells are similar to those descrit 

 by Lenhossek* and Retziusf in the earthworm, and by RetziusJ, ii 

 polychaetes and molluscs. They are spindle-shaped and lie in 

 ectoderm (or immediately beneath it) of the dorsal surface of 

 abdomen. The distal end of the spindle either runs out as a 

 fibre which ends freely, or the end of the fibre broadens out, fori 

 a T-shaped figure on the end of the spindle. The fibre arising 

 the proximal end of the cell passes forwards and downwards to tl 

 nerve cord, where, after entering one of the ganglia, it bifurcat 

 giving rise to a Y- sna P e ^ figure. One of the branches runs 

 wards, the other backwards along the ganglionic cord. They hai 

 been seen to pass through two ganglia, but as to where they end ! 

 am not at present in a position to make a definite statement. 



Theoretical. 



I shall now endeavour to draw attention to some points of ii 

 terest connected with the observations described above, 

 regard to the elements C and D, it might be maintained that tl 

 represent a purely embryonic arrangement, which has not 

 reached the active state. This, however, appears to me improl 

 from the fact that the two systems remain in practically the sat 

 state from very eai-ly embryos, in which the eye-pigment has jt 

 begun to deposit, to the oldest larvra (about one week) which I hai 

 been able to examine ; and also from the fact that they take 

 methylene blue in a way which, according to present experience, 

 active nerve tissue does. Assuming then that the system is in tl 

 active state, it is important to notice the position of the three tufts 

 fibres, which stand opposite to each other, where elements C and 

 end. Although my observations agree entirely with those of Retzit 

 Kolliker, and the majority of recent investigators, in the fact tlu 

 direct anastomosis of the portion of the element which stains wit 

 methylene blue has never been observed, it seems impossible 

 understand the meaning of this arrangement on any other snpj 



* Lenhossek, " Ureprung, Yerlauf, und Endigung der sousibeln Xerrenfasern 1 

 Lumbricue," ' Arch. Mikr. Anat.,' vol. 39, 1892. 



f Retzius, " Das Nerrenaystem der Lumbricinen," ' Biol. Unterauch.' "St 

 Folge III, 1892. 



t Ditto, Neue Folge IV, 1892. 



