ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
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nected with the cuticle by a slender stalk. The retina is looked upon 
as a single layer of epidermal cells, each of which has elongated in such 
a way that its nucleus has receded from the cuticle while the clear, 
cuticular end has fused more or less with that of the other cells to form 
the layer of rods, the lens, and (if present) the vitreous body. 
Anatomy and Histology of Serpula dianthus.* — Mr. A. L. Tread- 
well has made a study of this small worm by means of serial sections ; 
the original describer, Prof. Verrill, appears to have taken the dorsal 
for the ventral side and vice versa. Owing to the extraordinary develop- 
ment of the dorsal longitudinal muscles the animal, when coiled, has its 
dorsal side concave rather than convex, and this may have led to the 
error. The operculum is sometimes on the right and sometimes on 
the left side ; on the opposite side is a small pseudoperculum, which 
seems to be of a sensory nature. The external cilia found by Claparede 
in allied Annelids appear to be absent from this species, but in a number 
of characters it agrees with Spirographis Spallanzani as described by 
that well-known anatomist. The food consists largely, if not entirely, 
of diatoms. The nervous system is highly developed, and the cerebral 
ganglion has a diameter of 5 mm. in specimens whose whole body-dia- 
meter was 14 mm. ; it gives off anteriorly two large branchial nerves, 
two smaller oesophageal, and one posterior and median. There is a large 
circum-cesophageal commissure and a large ventral ganglion on either 
side. The ventral system is composed of two long nerves, swollen out into 
segmentally arranged ganglia which decrease in size from before back- 
wards. The tubular fibres are not so highly developed in S. dianthus 
as in allied forms, for they thin out and disappear in the first pair of 
ventral ganglia. 
The posterior dorsal portion of the cerebral ganglion is prolonged 
into a most remarkable process, for a large lobe passes outwards and 
backwards, and after a short course bends suddenly downwards and 
passes into the first ventral ganglion. They form, in fact, a second 
pair of oesophageal commissures made up almost entirely of nerve-cells, 
and giving rise, apparently, to no nerves. 
The tubiparous glands lie one on either side in the first body-segment, 
and open by a common duct ; they are much convoluted and have an 
internal duct which opens into the body cavity by an expanded elongated 
funnel. The ovaries are small rounded bodies, one on either side in 
each segment behind the middle of the body, and set close against the 
segmental septa ; the ova lie loose in the body-cavity, and completely fill 
it towards the hinder end ; the external openings are in the posterior part 
of each segment, are small and surrounded by a thin lip made up of 
hypoderm, muscles, and peritoneum, greatly reduced in thickness, and 
of a special layer of circular muscles. The arrangement is such that a 
contraction of the body-muscles would open and that of the circular 
muscles would close the orifice. No male specimens have yet been 
seen. 
Protective Device of an Annelid, j — Mr. A. T. Watson describes a 
Sabellid worm in which the tube, on the retreat of the contained 
* Zool. Anzeig., xiv. (1891) pp. 276-80. 
f Nature, xliv. (1891) p. 507 (3 figs.). 
