136 



LIBBIE H. HYMAN 



but is usually hypoineric. The percentage of such heads is 



small in pieces from anterior regions, but increases along the axis. 



S. Aprostomic heads. This type of inhibited head consists 



of a rounded outgrowth, in which the prostomiuni is entirely 



d 



Fig. 20 Types of anterior outgrowths in Lumbriculus. a, normal head in 

 nature; b, normal regenerated head; c, two types of hypoprostomic heads; d, 

 two aprostomic heads, which are also markedly hypomeric; e, an acephalic con- 

 dition;/, cephaluran outgrowth; g, biaxial tails. 



lacking, (fig. 20 d). There is no mouth, the pharynx ending 

 blindly. Histological examination shows that the supraoesoph- 



