209 
the annulation; the parapodia and sete*; the gills*; the 
prostomium and nuchal organ; the peristomium and the 
succeeding achetous 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 
chetigerous 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 celomic fluid before 
proceeding with the dissection the first incision should be 
made while holding the worm in the hand over a watch 
glass. The ceelomie 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 below) 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 sete and gills is _ better 
deferred until later. See Sections VIT. and VITT. below. 
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