MUSEUM OF COMPARATIVE ZOOLOGY. 207 



PLATE VI. 

 Aricidea, Nereis, and Unknown Genera. 

 m. Mouth. pr. Ring-shaped pigment regions on ventral side 



m s. Mandibles. of body. 



mt. Median tentacle. <J- Two ventral pigment spots on fourth body 



ce. (Esophagus. »'• Dorsal pigment bands. [segment. 



Fig. 1. Larva of ^r/c/c^ea (dorsal view). 



" 2. Unknown Annelid larva with two ventral pigment spots. 



" 3. The same, slightly older. 



" 4. 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. 



" C)K Head and jaws of the last. 



" 7. Larval Annelid with pigmented ventral rings, described in the text as 



polytrochal larva (ventral view). 



" 8. Tlie same, dorsal view. 



" 9. The same, lateral view (head represented downward). 



*' 10. Larva of Aricidea more advanced than that shown in Fig. 1. 



PLATE VII. 



Lumbriconereis. 



a p. Anterior pole. ma. Macromeres. 



(I r. Anterior body region. mi. Micromeres. 



cb. Ciliated band. nc. Ventral nerve cells. 



(•/). Caudal pigment spots. ce. GCsophagus. 



i. Intestine. pp. Posterior pigment spots which ultimately 



j. Jaws. become the caudal pigment spots, cp. 



I o. Lateral ocelli. s. Stomach. 



I p. Lateral pigment spots. z. Unknown organ developed from stomach. 



7/1. Mouth. 



Fig. 1. Egg of Lumbriconereis, 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. Tlie large macromere 



cells are to be seen in the middle of the larva througli its walls. 

 " 3. 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. 

 " 5. The same larva, a little older, in wliicli lateral pigment spots, as well 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. 



