SMALLWOOD. — POLYCERELLA ZOOBOTRYON. 



613 



to 60 micra in length and 1.4 to 3 micra in diameter. Each spicule is 

 rounded at the ends and has a number of spiny enlargements. The 

 largest spicules (Figure 2) are found in the foot. Their arrangement 

 does not follow any plan, except that in the rhinophores and the 

 several integumentary processes they are mostly parallel to one 

 another. 



2. Anatomy of Digestive System. 



The mouth opens by a vertical slit directly into a short passage 

 about 10 micra long, the buccal cavity (Figure 4, cav. hue). The pos- 



FiGTJKE 3. Diagram showing the general topographical relations of diges- 

 tive, reproductive, and renal systems as seen from above, atr.gen., genital 

 atrium; bb.suc, suctorial bulb; cam.ren., kidney chamber; ga.-int., stomach- 

 intestine; gen.a., anterior genital mass; gen.p., posterior genital mass; oes., 

 esophagus; par.so., body wall; ren., kidney; urt., ureter. 



terior part of this passage expands to form the pharynx, into the 

 posterior end of which open three hollow organs ; ventrally the ante- 

 rior end of the radula sac {sac. rad.) ; more dorsally, the esophagus 

 {oes.); and still more dorsally, the cavity of the suctorial bulb {bb. sue). 

 The walls of the buccal cavity are largely composed of muscles and 

 have a thickness of 12-15 micra. The dorsal portion of the buccal 

 cavity is directly continuous with the enlarged suctorial bulb, the wall 

 of whose fundus often attains a thickness of .30 micra. The posterior 

 wall is not more than one half as long as the anterior. The distance 



