MUSEUM OF COMPARATIVE ZOOLOGY. 207 
PLATE VI. 
Aricidea, Nereis, and Unknown Genera. 
Mouth. pr. Ring-shaped pigment regions on ventral side 
. Mandibles. of body. 
. Median tentacle. g. Two ventral pigment spots on fourth body 
Csophagus. r. Dorsal pigment bands. [segment. 
Larva of Aricidea (dorsal view). 
Unknown Annelid larva with two ventral pigment spots. 
The same, slightly older. 
The same, older (Figs. 2, 3, 4, ventral view). 
4°. Side view of Fig. 2, showing the prominence (g) upon which the ventral 
pigment spot is borne. 
4>, Side view of ventral prominence in Fig. 4. 
5. Unknown pelagic worm larva. 
6. Larva of Nereis. 
6*. Head and jaws of the last. 
7. Larval Annelid with pigmented ventral rings, described in the text as 
polytrochal larva (ventral view). 
The same, dorsal view. 
9. The same, lateral view (head represented downward). 
10. Larva of Aricidea more advanced than that shown in Fig. 1. 
hav igedbs: ap 
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PLATE VII. 
Lumbriconereis. 
. Anterior pole. ma. Macromeres. 
Anterior body region. mi. Micromeres. 
Ciliated band. ne. Ventral nerve cells. 
:p. Caudal pigment spots. e«.  CXsophagus. 
Intestine. pp- Posterior pigment spots which ultimately 
Jaws. become the caudal pigment spots, cp. 
Lateral ocelli. s. Stomach. 
Lateral pigment spots. z. Unknown organ developed from stomach. 
Mouth. 
1. Egg of Zumbriconereis, in which the micromeres have almost wholly 
surrounded the macromeres. 
2. Larva of Lumbriconereis, in which the anterior prominence (a p), the ciliated 
band, and the external layer have formed. The large macromere 
cells are to be seen in the middle of the larva through its walls. 
8. Still older larva of the same, more elongated, and with the anterior 
prominence pointing to one side. 
4, Larva of Lumbriconereis, in which the internal large cells are less distinct, 
and in which cephalic and caudal ocelli have appeared. 
The same larva, a little older, in which lateral pigment spots, as oe as 
those mentioned in the preceding figure, are seen. 
6. A larva still older, the caudal segment of which has begun to lengthen 
into the future body of the worm. 
on 
