88 
ZOOLOGY OF THE FAR EAST. 
Fam. NAIDIDAE. 
Chaetogaster annandalei, sp. nov. 
N. Lake, L,. Biwa, Japan ' ; 15 ft. In Spongilla lacusiris, growing on leaves of Potamogeion. 
2g-ix-igi5. 
The sponges did not apparently form a very favourable residence for the worms : 
they were young and compact, and the worms were few, — none might be found on 
teasing up a whole sponge. Had the sponges been older and disintegrating the 
Chaetogasters might have been more numerous. 
The worms are minute, a single individual being only 44 mm. in length, and a 
chain of two '66 mm. In diameter they measured '13 mm. n=io or 11. 
There is a well-marked prostomium, i.e. the anterior end of the animal extends 
forward in front of the margin of the mouth aperture, which is thus on the ventral 
surface; in a number of the other species of the genus the anterior margin of the 
mouth coincides with the tip of the snout. The prostomium is here a bluntly triangu- 
lar projection. 
There is a distinct constriction behind the second segment, and thus the appear- 
ance of a head is produced; this " head " is small, about two-ninths of the length of 
the animal (or of the first animal of the chain), and rather conical in shape, broadest 
behind. The appearance is given of a fairly strong septum behind the "head," but 
this was not confirmed in sections. 
There are no dorsal setae. The number of setae in the ventral bundles is 
small, 4 or 5 in the second segment (where they are directed forwards), and 3, or 
often only 2, in the hinder part of the body. They are absent, as usual, from 
the third to the fifth segment inclusive. In length the setae of the second seg- 
ment measure yo/x^ and those of the other segments 50 to 6o/x ; in thickness they 
are about i'5//. They are double-pronged, but the prongs are ver}^ fine and not 
distinctly visible with the ordinary high power of the microscope ; with the oil 
immersion they are seen to be of unequal length, the distal being the longer and 
more curved. The shaft is only slightly and gently curved at both ends ; the 
nodulus is markedly proximal to the middle of the shaft, the proportions being 
about 3:4. 
The oesophagus is quite short, and is succeeded by a much dilated "crop," the 
hinder part of which is opposite the setae of segment vi ; or the chief swelling of the 
alimentary canal may be posterior to this, so that there is a small "crop" and a 
large ' ' stomach . ' ' 
The heart is situated dorsal to the oesophagus, in segment iii or in iii and iv. 
There is apparently no refractile bodj^- in the cerebral ganglion, such as has been 
noticed in a number of the other species of the genus. 
Remarks. The minute size of the animal, together with the short oesophagus and 
the small number of setae per segment, will suffice to distinguish the present form. 
' Since the above account was written I have found the same species, also from a sponge, in a collection made by 
Dr. Annandale at the Inl^ Lake, Southern Shan States. 24-iv-i9i7. 
