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Nerve Elements of the Embryonic Lobster. 
By 
Edgar J. Allen, B.Sec.Lond. 
Arter repeated trials with dilute solutions of methylene blue upon 
larvee and embryos of a number of the smaller decapod crustacea, a 
favourable object for the study of the nervous system was at last 
found in the embryo of the common lobster. The embryos of this 
animal are specially advantageous on account of their large size, 
which enables them to be readily manipulated without much damage 
being done to their tissues, and also on account of the large size of 
the individual nerve elements. 
In order to expose the ganglionic cord in the thorax, it is only 
necessary to break the yolk with needles and carefully remove it. 
If the embryo thus prepared be placed with the dorsal surface of 
the cord uppermost in a dilute solution of methylene blue in sea 
water (1 : 50,000 or 1: 100,000), stainmg of one or more nerve 
elements takes place. 
By practismg this method upon a large number of embryos at 
various stages of development, staiming of the following elements has 
been obtained : 
1. Elements starting from cells in the brain or anterior thoracic 
ganglia, and giving off fibres which can be traced throughout the 
length of the ganglionic cord to the sixth abdominal ganglion. The 
fibres of some of these elements pass down the cord upon the same 
side as that on which the cell 1s situated, whilst others decussate and 
pass down upon the opposite side. Many of the fibres give off 
collateral branches to the neuropile of each ganglion through which 
they pass. One pair of fibres belonging to this group are the 
so-called giant fibres. They possess a diameter many times greater 
than any other fibre in the cord, and start from a cell which hes on 
the ventral surface of the brain. In the sixth abdominal ganglion 
these fibres break up into a number of smaller branches. 
2. Klements originating in a cell in one of the gangha of the 
cord, from which a fibre is given off, which after decussation with its 
