276 MENSCH. [Vol. XVI. 



found in most of the specimens, and may be regarded as the 

 rudimentary representative of this cirrus. 



The head is less emarginate in front than that of the Poly- 

 bostricus, has a median (d.m.), and but a single pair of lateral 

 tentacles {a. I.), and is very similar in appearance to the head of 

 the parent stock. Palps and the posterior lateral tentacles are 

 absent, and the anterior lateral tentacles are not thickened and 

 bifurcated, as in the male stolon. 



The fully matured Sacconereis carries on its ventral side an 

 egg-sac {o.v.) filled with eggs. This sac consists of a thin 

 membrane attached to and formed from the tissue of the under 

 surface of segments 4 to 8 or 9. The anterior part of the body 

 as far as, and sometimes including, the fourth setigerous seg- 

 ment is free, as are also the segments posterior to 8 and 9. 

 When the animal is at rest the free portions of the body are 

 usually coiled around the egg-sac in a spiral manner, in this 

 way forming a protection for the delicate sac. When in motion, 

 however, the free regions of the body are fully extended and 

 the egg-sac bulges considerably both ventrally and laterally. 

 The color of the less mature eggs is bright red ; but as they 

 become more fully matured they assume a darker and almost 

 black appearance. 



In comparing the head structure of the mature male and 

 female stolons with those of the parent stock it is evident that, 

 with the exception of the fusion of the palps with the anterior 

 lateral tentacles, the presence of the posterior lateral tentacles 

 in the male, the absence of palps and dorsal tentacular cirri in 

 the female, and the shifted position of the anterior eyes, the 

 head parts of the stolon are an almost exact reproduction of 

 the head parts of the parent stock. 



The movements of these free stolons as compared with those 

 of the parent stock are very active, and notwithstanding the 

 size of the egg-sac, the mature Sacconereis is able to move 

 about with great agility. 



Sexual Characteristics of tJie CJiain of Stolons. — The chain 

 of stolons is always unisexual, all stolons of a chain being 

 either male or female. The sex of the chain can, even in very 

 young stolons, be distinguished by the bifurcation, in the male, 



