ANNULATA. 233 



271. There are several other groups of annulates of considerable inter- 

 est to the zoologist which it seems necessary to pass by with mere 

 mention. 



Class: Archi-annelida ; a few primitive forms, as Polygordius (Fig. 

 104). 



Class: Sipunculoidea (Gephyrea'}. With traces of segmentation in 

 the embryo, but not in the adult. 



Class: Chsetognatha (arrow worms). 



Some authors would place here also the Rotifers (see 230). 



272. Suggestive Studies for Library and Laboratory. 



1. Look up the characteristics of the Archi-annelida, the Gephyrea, or 

 Sagitta, and report on their likenesses to the types studied. 



2. On what grounds might the rotifers be associated with the annulata? 



3. Compare the " segments " in cestodes and annulata. 



4. In the Chsetopoda which sets of organs pass through all the seg- 

 ments, which are repeated in essentially all, and which are limited to a 

 few? 



5. Examine and report on the habits of the earthworm. (Study in its 

 natural haunts or in box of moist earth in laboratory.) What are its 

 haunts? Method and rate of burrowing? Does it avoid water? What is 

 its food? How taken? Does the animal prefer light or darkness? 



6. If near the sea-shore select other forms and report in a similar way. 



7. Investigate parasitism among the Annulata. 



8. What is the economic value of the earthworm? Of other worms? 



9. Make a study from the text-books of the reproductive organs in any 

 of the hermaphrodite Oligochaeta. 



10. In how many species of aquatic Oligochseta do you find reproduc- 

 tion by fission? In what particulars does the process seem to differ in 

 the different species? 



11. Outline the life-history of Autolytus, including the origin of the 

 sexes. 



