98 ANNELIDA 



sition of the elytra are also characteristic of various genera, 

 and may be conveniently represented by an elytral formula 

 consisting of the numbers of the somites on which elytra are 

 borne, e. g., 2, 4, 5, etc. Determine the elytral formula of 

 your specimen. Draw one of the elytra, noting its form, 

 surface, and border markings, etc. These points are of im- 

 portance in defining species. Each of the last pair of elytra 

 is notched on the medium side over the anus, which in this 

 form opens dorsally instead of terminally. 



DIOPATRAICUPREA 



This worm belongs to the family Eunicidae. Specimens 

 live on mud and sand flats, sometimes above low-tide mark, 

 but usually where the burrows are covered by water. This 

 form is especially interesting because of its feeding and tube- 

 building habits, parapodial gills, and complex jaw apparatus. 

 Study the preserved specimens for the structure and speci- 

 mens in an aquarium for the habits. 



Make a special, comparative study of the reactions of 

 Nereis and Diopatra. What types of movements can you 

 distinguish? What is the significance of each? Which worm 

 is better adapted for a pelagic life? Locate any respiratory 

 structures which may be present. What structural differences 

 can you see which may be correlated with different habits? 

 Place a glass tube in the dish with a worm and gently move 

 the head of the worm so that the anterior end projects into 

 the tube. Observe results. Study the activities of a worm 

 after it has been in the tube a few minutes. Are these iden- 

 tical with the movements of the worm when free in the 

 water? Supply a Diopatra in a glass tube with bits of sea 

 weed or shells and observe the method of tube formation. 



1. Notice the size of the body, also its gradual attenua- 

 tion posteriorly. Account for this condition. Observe how 

 degenerate the posterior parapodia are from the same cause. 



2. The prostomium. Identify the tentacles. What is 

 their number and arrangement? Find a pair of eyes dorsally 



