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Messrs. Hancock and Embleton on the Anatomy of Eolis. 189 
them, and the commissures, excepting the modifications to be 
presently mentioned, are pretty much the same, as far as we have 
been able to examine them, as they exist in E. papzillosa. 
In E. coronata the olfactory tractus are much shorter, and 
their ganglia more globular, and of much greater relative size 
than in EL. papillosa, being indeed more than one-third the size 
of the lateral supra-cesophageal ganglia themselves. There is 
besides one principal nervous stem from the ganglion which runs 
up the central axis of the tentacle. 
In EZ. Drummondi the relative size of these ganglia is still 
greater and their form elliptical. The existence of these ganglia 
we believe to be constant in all the species ; we observed them in 
E. pellucida, E. Farrani, E. alba, E. gracilis, E. picta, E. pune- 
tata, &c. 
The three nervous collars of the cesophagus can be observed 
easily in LH. Drummondi, in which there appears to exist at the 
coming off of the genital nerve from the middle or slender collar 
a small ganglionic swelling @. A similar swelling occurs also in 
E. coronata. 3 
When viewed attentively with the naked eye, the cerebral 
ganglia, and particularly the first or median pair, present a num- 
ber of large globular vesicles inclosed within a transparent mem- 
branous envelope. When compressed and somewhat magnified, 
all the ganglia seem to be made up of masses of vesicles, as the 
view of a buccal ganglion, Pl. VI. fig. 2, will show. Under a 
higher power these vesicles or cells are found of very variable 
size, externally smooth, internally granular, and having one or 
more large distinct nuclei and nucleoli; some have only one large 
nucleus and a distinct nucleolus ; the interior is filled with smaller 
cells of different dimensions and also nucleated; the smallest of 
all however are minute, clear, bright cells, probably nuclei or 
rather nucleoli of larger vesicles. Many of these last are found 
also lying in the intervals of the large cells intermixed with the 
tenacious semifluid matrix that imbeds the nervous vesicles, and 
in which no distinct forms can be discerned. On tearing up one 
of the cerebral ganglia and examining the contents of the mem- 
branous envelope in the compressor, under a high power (one- 
eighth object-glass), numbers of the cells of all sizes are seen 
under the form of pear-shaped, largely nucleated vesicles, Pl. VI. 
fig. 4, having a long pedicle attached ; the nucleus, which is very 
large, has an evident and well-marked nucleolus, and the pedicle 
or stalk of the cell is in the interior very finely granular. Groups 
of these pedicled ovoid vesicles may be observed, such as that at 
Pl. VI. fig. 3, their pedicles all lying in the same direction, and 
tending either to unite or to run on parallel to each other, put- 
ting us strongly in mind of some of the simpler forms of glan- 
