SEA-FISHERIES LABORATORY. 289 



the aiinulation ; the parapodia and setse* ; the gills* ; the 

 prostomium and nuchal organ; the peristomium and the 

 succeeding achsetous segment ; the external apertures, the 

 mouth, anus, nephridiopores, and apertures of otocysts. 



Dissection. 



Extend the animal under sea water with the dorsal 

 surface upwards, fixing it down by two pins through the 

 sides of say the first segment, and two through the sides of 

 one of the posterior branchial segments. Open the 

 animal by making an incision with fine scissors along the 

 mid-dorsal line, beginning about the middle of the 

 chsetigerous portion. Raise the flaps gently with the 

 forceps and extend the cut anteriorly to within about an 

 eighth of an inch of the prostomium, and posteriorly 

 about an inch into the tail. The tail is difficult to open 

 satisfactorily, unless great care be taken the alimentary 

 canal will be cut open with the body wall. The flaps of 

 the body wall should be regularly pinned out right and 

 left so that the animal is moderately well stretched both 

 longitudinally and transversely. 



If it is desired to examine the coelomic fluid before 

 proceeding with the dissection the first incision should be 

 made while holding the worm in the hand over a watch 

 glass. The coelomic fluid which at once escapes through 

 the cut must be examined immediately, as on standing 

 even a short time the corpuscles collect into clots. 

 Examine the fluid fresh and determine the sex of the 

 specimen. A few permanent preparations (for method 

 see p. 293) are also useful. 



At the breeding season the ova and masses of sper- 

 matids are so abundant as to partially obscure some of the 



* The detailed examination of the setse and gills is better 

 deferred until later. See Sections VII. and VIII., p. 292. 



