GENERAL BIOLOGY 



worm, and then gently squeezing it, when a small drop will come 

 out of the openings, (c) Sexual apertures, (i) Openings of 

 spermaducts, or vasa def erentia ; two openings surrounded by 

 swollen areas on the ventral surface of the i5th somite. From 

 these openings, grooves are often found passing back to the clitel- 

 lum. (2) Openings of oviducts ; two small pores on ventral surface 

 of the I4th somite. (3) Openings of the seminal receptacles or 

 spermatheca, two openings on each side between the 9th and loth, 

 and loth and nth somites, in line with the outer row of setae and 

 posterior to them, (d) Nephropores ; openings of the segmental 

 organs or nephridia ; two openings in each somite, one on each side, 

 just dorsal to the ventral pair of setae. 



Draw the anterior and posterior portions of the body to illus- 

 trate all that you hcwe observed. 



B. INTERNAL ANATOMY. 



Extend the worm, ventral side down, in a dissecting pan, and 

 fasten firmly by a pin at each end (the anterior one through the 

 prostomium only) ; cover with water, and cut open carefully 

 from behind forward with fine scissors making the incision along 

 the dorsal side a little to one side of the dorsal median line. Do 

 not cut deep, but merely through the body wall. Carefully cut 

 through the partitions or septa along each side, stretch out the body 

 wall to right and left, and fasten with pins. 



Observe the following structures, dissecting as little as possible 

 to make them out : 



I. GENERAL FEATURES. 



1. Body wall, thick and firm and composed of three layers: 

 (a) A thin cuticle on the outside; (b) a more or less colored 

 layer, the epidermis ; (c) a light-colored, and much thicker layer 

 internal to the epidermis, the muscular layer. 



2. Body cavity or coelum, with the digestive tract passing 

 through it from mouth to anus, and septa or transverse partitions 

 dividing it into as many chambers as there are somites. Each sep- 

 tum passes from the digestive tract to the body wall. What is the 

 relation of the septa to the external grooves? 



3. Seminal vesicles, large lobed bodies between the io!h and 

 1 5th somites, partly covering the digestive tract. 



4. Dorsal or supra-intestinal blood vessel, generally full of 



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