412 THE LANCELET chap. 



5. The _q;clalinous connecLive tissue forming ihc Ji//- raj' ■•-. 



6. The iiitcsiiiic, with its sint^lc layer of lung cpiLhciial culls. If the 

 section j^asses ihrough (he anus, the laller will lie seen opening on the 

 left side of Ihc ventral fin. 



7. The iolouie, surrounding the intestine, and aKo enclosing the 

 ^iihiiitcstinal or portal -,'cius (Fig. lOl). 



S. The dorsal aorta^ just below the nolochord. 



b. do over 2, 3, 4, 5, 6, and 8 again — all mucli as in a. Note^ 



1. ThQ dorsal -^vkX lal>'ral fins [i/ie/apleural folds), ventral body-wall, 

 small melapleural lymph-canals, and airiopore^ if present in your section. 



2. The i{YJo»it\ a narrow space round the intestine, in which three or 

 fuur subiiitt'siinal {portal) rvv/^f can he seen. 



3. The a/rial cavity just outside the ccelome, and separated from it 

 by \\\c atrial iiienibranc. If the section passes through the atriopnre, 

 it will be seen in the mid-ventral line, putting the atrial cavity in com- 

 munication with the exterior. 



L Note— I. The triangular form of the body in transverse section; 

 the dorsal fin, the ventral surface, with its folded integument and thin 

 transverse ventral muscles ; the metapleural folds and their contained 

 large canals. Then go over a. 2, 3, 4, and 5 again, which are all much 

 as in a an<l b. 



2. The ///(?/ j;m', lying just below the notochovd, and extending nearly 

 to the ventral body walls. Note — [a) the deep, dorsal epihrauihial 

 groove: [b) the ventral i?/^f/(',r(y/i^ projecting into the pharyngeal cavity, 

 and enclosing a crelomic canal ; (c) the gill-bars, a great number of 

 which will be cut thr<.)iigh obliquely, longer primary alternating with 

 smaller secondary ow^:-^. Note the skeletal rods near their outer surfaces, 

 and, in the primary bars, the small CQ^loiuic spaces on the outer sides of 

 the ro(K ; {d) the dorsal suspensory folds of the pharynx, which encliise 

 the two dorsal co'lo)nic canals. 



3. The atrial cavity, surrounding the pharynx except at the mid- 

 dorsat line where the ]^harynx is attached to the sheath of the noto- 

 chord, and communicating with the cavity of the pharynx through the 

 gill-slits. It is enclosed by the two at rictl folds, which are united in 

 the mid-ventral line ; the atrial epithelium is often much folded vcn- 

 trally. 



4. The single 7'eiifral aorta, in the endostylar crelomic canal, and the 

 paired dorsal aortcp, on either side of the cpibranchial groove. 



d. Note again- a. 2, 3, 4, 5 ; . . i, 3, 4, and also ; 



