356 THE EARTHWORM CHAP. 



with the high power. Note that the nephridium consists of a long 

 coiled tube, plentifully supplied with blood-vessels, and that long 

 vibratile cilia can be seen in parts of it. (For details see VI.) 



Add a little methylated spirit to the water in your dissecting dish and 

 sketch your dissection. 



5. The ovaries. Examine segment XIII closely, being very careful 

 not to injure its contents, and the ovaries may then be seen projecting 

 backwards into this segment, one on either side, just in front of the 

 crop. They can easily be recognised by their shape, and by the fact 

 that they hang freely into the ccelome, as can be seen by touching them 

 with a seeker. Carefully seize the septum between segments XII and 

 XIII with the small forceps, and cut around the attachment of an 

 ovary so as to remove it. Stain with methyl-green or magenta, and 

 mount in glycerine (or else fix, stain, and mount in balsam, as directed 

 on p. 136). Note the mass of undifferentiated cells at the proximal, at- 

 tached end of the ovary, and the gradual development of the ova 

 towards the distal, narrower end. Examine an ovum, and observe the 

 nucleus, nucleolus, and granules of food -yolk. Sketch the ovary. 



(The oviducts and ovisacs are not easy to make out in dissec- 

 tions, but the latter may be recognised by their red colour. ) 



6. The globular spermotheca (usually two pairs) in segments IX 

 andX. 



III. Tease out a small portion of a sperm-sac, stain with magenta, 

 and mount in glycerine. The following stages in the development of 

 the sperms can then be made out : a. the sperm-mother-cells or 

 gametocytes (developed in the spermary) in different stages of division ; 

 the products of division, each with a nucleus, and arranged in a 

 single peripheral row, the central mass of protoplasm remaining un- 

 divided ; b. the gradual elongation of these small cells ; and c. the 

 conversion of each into a sperm., the nucleus forming the rod-like 

 "head," and the protoplasm giving rise to the delicate " tail ; " d. free 

 sperms (also to be found in the spermotheoe ; some of them should be 

 examined fresh and their movements noted). Sketch a series of stages. 



It is difficult to make out the two pairs of sperniaries and the 

 spermiducts by dissection, and they can be more easily studied by 

 examining transverse sections, prepared as directed in C. (In Lum- 

 bricus the spermaries and seminal funnels are enclosed within the 

 median sperm-reservoirs, Figs. 82 and 86. ) The spermiducts are partly 

 embedded in the body-wall. 



