ix PRACTICAL DIRECTIONS 427 



between the members of a pair, the rods of these being unsplit 

 ventrally. Note also the horizontal bars connecting the 

 primary and secondary gill-bars and making the walls of 

 the pharynx appear like a mesh work. 



6. The cavity of the oral hood, bounded by lateral folds, 

 the muscular velum between it and the pharynx, and the 

 minute mouth. 



7. The intestine, running straight from the hinder end of 

 the pharynx to the anus, and giving off near its anterior 

 end the hepatic ccecum or " liver " extending forward on the 

 right side of the pharynx. 



8. The myomeres and the intermuscular septa between 

 them, arranged like a series of V's, the apices of which 

 point forwards. The muscular fibres run longitudinally 

 from septum to septum, and are of the striped kind. 



9. The gonads (ovaries or spermaries], arranged in a single 

 row on either side of and also rather further back than the 

 pharynx extending as far as the atriopore. Note in the 

 female the large ova, which, when ripe, cause a great disten- 

 sion of the body ; and in the male the minute sperm-cells, 

 the structure of which cannot be made out in entire speci- 

 mens. Sketch. 



II. Cut a specimen into short pieces, about an eighth of 

 an inch in length, and select portions from a, between 

 the hinder end of the atrium and the anus (Fig. 109, B), or 

 through the latter ; b, just in front of or through the 

 atriopore ; c, through the anterior part of the pharynx ; 

 and d, through the posterior part of the pharynx (Fig. 109, A). 

 Stain and embed these, and prepare a few sections from 

 each (see p. 136). Examine in the order given above, first 

 with the low, and then with the high power. Sketch a 

 section from each region. 



a. i. The oval form of the section, the median dorsal 

 and ventral fins, and the integument (columnar epiderm and 

 thin derm). 



2. The myomeres cut across in various planes, and appear- 

 ing as squarish masses separated by the septa. 



3. The central notochord, oval in transverse section, with 

 transverse wavy lines indicating the boundaries of the 

 vacuolated notochordal cells. It is surrounded by a 

 connective-tissue sheath, continuous with the connective- 

 tissue investment of the neural canal above and with the 

 intermuscular septa at the sides : the latter pass into the 

 derm peripherally. 



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