AMPHITRITE ORNATA. 93 



faces are grooved and supplied with cilia, as is the median dorsal 

 line. Hence a current of water passes continually toward the 

 mouth. The twelfth somite is marked by a dorsal and a ven- 

 tral sucker, which are modified parapodia. Somites thirteen, 

 fourteen, and fifteen carry notopodial folds or fans, for keeping 

 up a stream of water through the tube. Their neuropodia are 

 mere knobs. 



3. The posterior region is less highly modified. Of how 

 many segments does it consist? Notice their gradual diminu- 

 tion in size. Homologize the parts of their appendages. 



4. The living Chsetopterus contains a green coloring-matter 

 and is very phosphorescent. A commensal polynoid often lives 

 in its tube. 



5. The eggs are orange yellow and the sperm milky white. 

 Determine their location. The sexes are separate. 



A drawing is desirable. 



Lillie: Observations and Experiments Concerning the Elementary Phe- 

 nomena of Embryonic Development in Chsetopterus. Jour. Exp. Zool., 

 3, 1906. 



AMPHITRITE ORNATA. 



This belongs to the family Terebellidse and lives under stones, 

 or in mud or sand, along shore in stout muddy tubes. 



1. Find the prostomium, which forms an upper lip and bears 

 a transverse group of long, retractile tentacles. 



2. The peristomium forms the under lip, but bears no appen- 

 dages. 



3. Find three pairs of racemose gills. These are modifica- 

 tions of the dorsal cirri. (Terebella has three pairs, but they are 

 of unequal size.) 



4. Notice again the feeble development of the parapodia 

 and the absence of ventral cirri and neuropodial setae. Setae 

 are not found posteriorly. On what somite do they begin? 



5. Find the ventral shield glands which are concerned in 

 building the tube. How many are there? 



6. The live worm is of a bright pinkish color, due to its red 

 blood. There is only one internal septum and it forms a so- 



