2 
W. J. Dakin 
The Tisceral ganglion of Pecten. 
Kawitz (1887) was the first and, so far as I am aware, is the only 
investigator who has made a detailed examination of the visceral gang- 
lion of Pecten. Unfortunately, and probably due to inferior methods 
of technique, there are several errors in his account, and his figures neither 
agree with his description nor with the actual structures. 
Drew (1906) also noticed the complexity of the gangüon, and point- 
ed out the need of detailed work on this subject, but he does not go into 
the matter himseK, nor does he refer at all to Kawitz, so that the State- 
ments of the latter are the only ones at present published. 
A study of the anatomy of Pecten, reveals the fact that that portion 
of the body usually innervated by the visceral ganglion in the lamelli- 
branchs has developed in this genus to a remarkable extent, whilst at 
the same time, a correspondingly great reduction of the anterior part 
of the animai has taken place. 
The anterior adductor muscle has disappeared, the posterior adductor 
has taken up a central position, the anterior region of the mantle lobes 
has become very small in extent, and the foot itself is rudimentary in 
the adult. We are not surprised then, to find that the visceral ganglion 
is of an advanced type and very large compared with the cerebral and 
pedal ganglia whose Innervation areas have been so reduced. 
The gangUon is situated in the usuai position, on the ventral surface 
of the adductor muscle and can just be seen through the connective tissue 
by reason of its yellow pigment. It lies imbedded (unfortunately) in a 
mass of connective tissue, somewhat to the right of the median line and 
a short distance anterior to the last point of attachment of the visceral 
mass; that is rather postero-ventral to the opening of the right renal 
organ. Though it can be seen, no details of its shape can be made out 
without removing the connective tissue, and this is not an easy matter. 
The plan adopted was to remove a slab of the muscle in the centre of 
whose surface the ganglion was situated and to leave the whole in 2 V2 — 
5% formol in sea water for 24 hours or longer. It was then rather easier 
to pin out the piece under water and to dissect away the overlying tissue. 
It was found impossible to foUow out the finest nerves without serial 
sections though some Information was obtained by dropping a little 1% 
osmio acid solution on the ganglion and nerves, after removal of the 
connective tissue. Bouin's Fluid and Zenker's Mixture have been satis- 
factory as fixatives and Mann's methyl blue eosin was used as a stain 
after the former. This is a very successful stain for nerve and connective 
