716 PROCEEDINGS OF THE ACADEMY OF [DeC. , 



form. This is seen in fig. 56, a slightly younger stage, drawn 

 from life. It is likely that several or many ova ripen in one gonad 

 tit once, and not one at a time as in many Nemerteans. 



The cytoplasm of this oldest stage stains a bright pink with the 

 hiematoxylin-eosin stain, and is charged with yolk; the nucleus is 

 very large, its diameter being about half that of the cell, the greater 

 part of its contents still taking the plasma stain. The nucleolus is 

 either one large rounded body, usually placed peripherally, or it is 

 broken up into numerous small fragments, which lie around the 

 periphery near the nuclear membrane, fig. 61, n. Several vacuoles 

 of varying size are present in the nucleolus. 



The attempt has been made to determine whether there is any 

 priority in the ripening of the sexual products of either end of 

 the body. No difference in the respective ages of the gonads of the 

 two ends has been observed in the specimens studied. In any one 

 immature gonad different stages may be found, the youngest cells 

 lying pei'ipherally, attached to the gonad wall, the older cells 

 toward the centre and free. 



11. The Caudicle. — The caudicle, a term suggested by Mont- 

 gomery (1897 a) as a translation of Burger's "Schwanzchen," may 

 be defined as the slender, thread-like process at the posterior end of 

 the body of certain Heteronemerteans." 



The caudicle of Zygeiipolia in life, figs. 4, 5, 6, appears as a 

 slender white filament, and a low magnification reveals a ciliated 

 surface and what seems to be a quite regular segmentation. A 

 closer examination, however, shows that the apparent annular 

 constrictions are merely the result of muscular contractions, and 

 are constantly varying in size and position. A light area along 

 the mid-line, bordered by denser areas, indicates the presence of a 

 central cavity — the blood lacuna. 



In connection with the caudicle, a description of the position of 

 the organs in the extreme posterior end of the body may be of 

 interest. The division of the dorsal blood vessel into two has 

 already been mentioned, and the subsequent fusion of the four 

 vessels into a central blood space; the termination of the rhyn- 

 choccel; the disappearance of the gonads and the dorsal opening of 

 the anus. A short distance in front of the anus the lateral nerves 



^^ It will be shown in the historical review of the literature of the caudicle, 

 that the structure described as a caudicle by Montgomery (1897 «) is in 

 reality a regenerating posterior end. 



