1894.] of the Nervous System of the Embryonic Lobster. 411 



along the outer border of the neuropile. It ends in the brain, at a 

 point nearly as far forwards as the termination of B Thorax V, but 

 somewhat lateral to it. In this fibre also no collaterals have been 

 observed in ganglia other than that in which the element originates. 

 A similar element occurs in Thorax I. 



C. Elements of this kind are inserted in ganglia Thorax VII X 

 io fig. 1. Each consists of a small cell in the anterior portion of the 

 lateral mass of ganglion cells. The fibre, after taking a Z" sua P e( l 

 course through the nenropile, to which it gives off numerous arbor- 

 escent branches, turns backwards, and after running between a fibre 

 of Series D and the central mass of ganglion cells, ends in a tuft of 

 fine branches at the posterior end of the ganglion next behind that 

 in which the cell is situated. 



D. These elements appear to be intimately associated with those of 

 Group C, and both groups generally stain in the same preparations. 



The cells of elements D lie in the posterior portion of the lateral 

 ganglionic mass. The fibre of each element passes forwards and 

 inwards through the neuropile, giving off numerous arborescent 

 branches to the latter. On entering the next ganglion in front, the 

 fibre has reached the outer border of the median ganglionic mass, and 

 after giving off a little tuft of branches in front of the tuft in which 

 one of the C elements ends, it pursues a direct anterior course, ending 

 in a tuft of branches in the ganglion next but one to that in which 

 i it started. This terminal tuft lies opposite the terminal tuft of one 

 of the C elements, and behind the lateral tuft of the D element of the 

 next ganglion. The three tufts lie at exactly the same level in the 

 cord, being all in the focus of the microscope at the same time. 



II. Elements consisting of a cell in the ganglionic cord, giving off a 



fibre, which, after sending arborescent branches to the neuropile, 



I passes out from the cord by one of the nerve roots. Many of these 



; elements, not improbably all, are motor, and in some cases the fibre 



has been traced through its whole course from the cell, until it breaks 



up on the muscle. (Fig 1, E. Thorax XI.) 



Typical elements of this class are inserted in fig. 1 (Thorax VII 

 XI, E J). Each of these ganglia contains one or more elements of 

 the various kinds. E and F have the cell situated in the lateral mass 

 of ganglion cells, and the fibre passes out through the anterior root of 

 the ganglion and goes to one of the limbs. In G and H the cell lies 

 in the central mass, but the fibre passes through the same anterior root 

 as E and F to a limb. The element J, on the other hand, passes through 

 the posterior root and goes to the muscles of the body wall. It arises 

 in a very small cell in the median mass, and the fibre runs for some 

 distance outwards. It then turns and takes a circular course through 

 the neuropile, forming a complete loop, after which it passes outwards 

 and enters the posterior nerve root. From the anterior part of the 



