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The Giant Nerve Cells and Fibres of Halla parthenopeia. 
By J. H. AsuwortH, D.Sc., Lecturer in Invertebrate Zoology in the 
University of Edinburgh. 
{Communicated by Professor J. C. Ewart, M.D., F.R.S. Received 
May 30,—Read June 18, 1908.) 
(Abstract. ) 
An anterior and a posterior series of giant cells are present in Halla 
parthenopera ; the following statement refers to the anterior series. 
The primary giant cells are formed in segmental couples—one couple in 
each of the anterior ganglia of the nerve cord—until a maximum of eight 
couples is attained. While the last three couples are being formed, 
secondary giant cells are also formed at the anterior end of the nerve cord 
and occasionally in one or more ganglia already possessing a primary couple 
The number of giant cells in full-grown specimens is usually 15 to 18, but 
specimens with 20 and 21 are recorded. 
There is a progressive increase in the size of the primary giant cells until 
the worm has attained a length of 30 to 40 cm., by which time the giant cells 
appear to have reached their maximum size. The largest cells are usually 
those of the second and third couples, which, in adult worms, are 130 to 150 pw 
in diameter. 
Yellow granules are present in the giant (and in some of the larger 
ganglion) cells, the substance and pigment of which are closely similar to, if 
not identical with, those of the chlorogogen granules. The granules in the: 
nerve cells therefore appear to be insoluble products of metabolism. 
Small, rounded, chromophilous granules are present in the protoplasm: 
(except in a peripheral zone, in which they are almost or quite absent) in 
varying amount in different giant cells. They are found in greatly increased 
mass in a specialised peri-nuclear zone, which is distinguishable in the living 
cell by its greater refringency. The outer edge of this zone is bounded by the 
peri-nuclear network of neurofibrille, which is thus in a position which 
facilitates its rapid nutrition. In many of the cells there is a “double 
nucleolus” which consists of one or more acidophile bodies enveloped by a 
basophile substance. 
Each giant fibre, after leaving the giant cell from which it arises, crosses 
the cord to the opposite side, turns gradually towards the middle line of the 
cord and runs posteriorly. Some of the largest fibres, from two to six in 
different specimens, run to within 1 or 2 mm. of the posterior end of the 
worm, the other fibres taper and successively disappear after running various 
VOL, LKXX.—B, 2P 
