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Additional Observations on the Nerve-Elements of the 



Embryonic Lobster. 



By 



E, J. Allen, B.Sc. 



Director of the Plymouth Laboratory. 



In Vol. III., No. 3, p. 208, of this Journal, a summary was given 

 of certain observations made in the Plymouth Laboratory on the nerve- 

 elements of the embryonic lobster. A more detailed description of 

 these elements, with figures, appeared in the Qitarterly Journal of 

 Microscopical Science, vol. 36, 1894. The observations have since been 

 extended, and the following summary of the additional results may not 

 be without interest. 



In the detailed paper a pair of elements (Element B) was described 

 occurring in the ganglia Thorax II., Th. V., and Th. VIII., each of 

 which consisted of a cell lying in the lateral mass of ganglion cells, 

 which gave off a fibre decussating with its fellow of the opposite 

 side, and then running forward to the brain. Before leaving the 

 ganglion in which the cell lay, the fibre gave off a pair of branches, 

 one going to the ganglion immediately in front, the other to the 

 ganglion immediately behind, the branches breaking up in the neuro- 

 pile of each of these ganglia. Thus Element B, in Th. II., sent a 

 branch to Th. I. and to Th. III. ; Element B, Th. V., sent branches 

 to Th. IV. and Th. VI.; Element B, of Th. A'lII., sent branches to 

 Th. VII. and Th. IX., the main fibres running forward to the brain. 



A precisely similar element has since been found in Th, XI., sending 

 branches to Th. X. and Abd. I., so that the series is now complete for 

 the thorax, and each of its ganglia appears to be influenced by these 

 elements, the fibres of which arboresce in a particular region of the 

 brain. 



A number of additional motor fibres, which cannot well be described 

 without drawings, have also been observed in the thorax, some of which 

 resemble those figured in the former paper, whilst others differ from 



