ARENICOLA CRISTATA. SABELLA MICROTHALMA. 85 



ARENICOLA CRISTATA. 



This remarkable worm, called the "lug-worm" by fisher- 

 men, belongs to the family Arenicolidae. 



1. Notice the color, and the gradual diminution in size pos- 

 teriorly. Also notice the false annulations between the appen- 

 dages, the arborescent gills representing modifications of certain 

 notopodia, the reduced parapodia, and the character of the setae. 



2. If the buccal region is everted, observe the papillae which 

 cover it. The prostomium is an inconspicuous dorsal knob and 

 it is fused with the peristomium. At the sides of the prostomium 

 is the ciliated nuchal groove. 



3. On what somites can you find indications of neuropodia? 

 of gills? of setae? Notice the cirriform papillae of the "tail." 

 Find large nephridiopores on certain somites about an eighth 

 o*f an inch below each notopodium. What is the distribution of 

 the pores? 



A drawing is desirable. 



SABELLA MICROTHALMA. 



This worm belongs to the family Sabellidae. It builds leath- 

 ery, muddy tubes on piles, among tunicates, algae, etc. 



1. In addition to the general size, form, and color of the 

 worm, observe the reduced condition of the parapodia, and the 

 arrangement and general structure of the branchice or gills. These 

 structures are modifications of the palps and not of the parapo- 

 dia, as in the other species which have been studied. Observe 

 the two irregular rows of small ocelli or eye-spots. Account 

 for the presence of eyes in their position. A pair of short tenta- 

 cles can be seen by spreading the branchiae aside. 



2. Find a collar which is used in smoothing the orifice of the 

 tube. This is a peristomial structure and is so extensively 

 developed in some species as to hide the prostomium entirely. 



3. Identify eight setigerous somites anteriorly, in which 

 the capillary setce are in the notopodium and the uncini are in 

 the neuropodium. With the peristomium they form a " thorax" 

 of nine somites. In the somites which follow, the "abdo- 



