: MUSEUM OF COMPARATIVE ZOOLOGY. 183 
longer, and additional segments have formed in the body, by which a still 
greater likeness to the adult worm has been acquired. It is still, however, 
free-swimming, although sometimes resting upon the bottom of the glass in 
which it is confined. The penultimate as well as the terminal body segments, 
are destitute of spines. The cesophagus has lengthened considerably, and 
through its walls the jaws (j) can be easily seen between the third and fourth 
segments.* The stomach walls are opaque and colored green. 
The “pigment dots” (k) found on the apex of the preoral lobe have now 
changed their position in the head, and moved somewhat backward towards 
the middle of the body. Each lies on the outside border of a transparent 
body of spherical shape, which touches on the median line of the larva a 
similar body on the opposite side. Both are situated in the dorsal walls, 
and are almost invisible when the larva is viewed from the ventral side. The 
rows of cilia about the neck are very active, as are also those near the posterior 
end of the body. The head retains its comparatively large size, and is without 
appendages. 
The next stage (Fig. 9) in the development of Nephthys shows us one where 
the reduction in the relative size of the head and body has gone on, and the 
cilia, which once formed such a prominent feature about the lower part of the 
former, have almost wholly disappeared. The head bears a single pair of short 
antenne. The body is composed of ten setiferous parapodia and a pair of ter- 
minal somites, which are without spines. The segments are separated by deep 
constrictions, and each parapodium is composed of a ventral and dorsal pro- 
tuberance, both of which bear serrated spines. The ventral cirrus is short 
and blunt ; the dorsal long and slender. 
The cesophagus has elongated to such an extent that its posterior end now ex- 
tends backward in the body cavity to the eighth segment. The “ eye-spots ” (/) 
lie in the dorsal walls of the third body segment. When the esophagus is 
protruded outside the mouth opening, these bodies retain their relative position 
as regards the segment, and are not moved with it, which indicates that they 
are not connected with the digestive tract, as might at first be supposed. The 
mandibles, with which they might be confounded, lie between the sixth and 
seventh segments, and can be protruded with the proboscis. 
The oldest larval Nephthys (Figs. 11, 12) which was observed has ten body 
segments which bear spines. I was able in one specimen to detect on the head 
the beginning of a single representative of a second pair of antenne, although 
such could be seen only on one side. In this larva, which is shown in Fig. 11, 
the head is quite small as compared with the body. The distance from the tip 
of one lateral spine on a body segment to the end of another, on the opposite side 
of the body, is three or four times the breadth of the middle of the body. The 
dorsal region of the head has a green color, in which are irregular patches of 
black and red. The black pigment probably later concentrates into those 
* In the oldest Nephthys, figured by Clapartde and Metschnikoff, they lie oppo- 
site the first body segment. 
