724 PROCEEDINGS OF THE ACADEMY OF [DeC. , 



measuring less than half the width of the body. The diminution 

 in size is due to the sudden disappearance of the outer longitudinal 

 muscle layer, and to the ending of the alimentary canal with the 

 body. 



A word must be said here in regard to the relative position of 

 the anus and the caudicle. 



Verrill (1893) states that the caudicle of the genus Mlcrura is 

 above the anus, and Coe (1895) says the same in regard to Cere- 

 hratulus lacteus. From my study of sections of Micrura coeca and 

 Cerebratulus lacteus I find that the anus undoubtedly opens dor- 

 sally above the caudicle, Nothing is easier than to confuse the 

 dorsal and ventral surfaces of a living worm, but in serial sections, 

 with definite structures for orientation, there can be no such diffi- 

 culty. The anus in Zygeupolia hkewise opens dorsally above the 

 caudicle, and Burger (1895) states that the dorsal position of the 

 anus is usual in Nemerteans. From these data it seems likely that 

 a thorough investigation of all species with caudicles will prove that 

 the dorsal position of the anus is of general occurrence. 



Burger (1895), p. 238, says in regard to the caudicle of Cerebra- 

 tulus, Micrura and Langia: " Morphologisch stellt das Schwanz- 

 chen uichts anderes dar als das stark und meist plotzlich verjiingte 

 hintere Korperende, in das sich von Organen der Darmtractus, 

 die drei Blutgefiissstamme, die Genitaltaschen und die Seiten- 

 starame fortsetzten, und in welchem wir auch alle Schichten der 

 Korperwand bis auf die Cutis, welche giinzlich verschwunden oder 

 in ihrer Ausbildung fast unterdriickt ist, antreff^en." According 

 to this all the organs of the posterior part of the body are repre- 

 sented in the " Schwanzchen," except the rhynchoccel, and even 

 this organ, Burger states, is present in the anterior part of the 

 caudicle of Cerebratulus marginatus. 



The observations of M'Intosh (1869) in regard to Mici-ura 

 purpurea^ those of Verrill (1893) on the whole genus Mier-ura, 

 and my own upon M. cceca are contradictory to the above state- 

 ment of Burger. In like manner Coe's work upon the American 

 species of Cerebratulus and my own upon the one species Cerebra- 

 tulus lacteus show that the caudicles of these forms cannot be 

 regarded as merely " verjiingte hintere Korperenden." From the 

 very limited space devoted to the subject of the caudicle in Burger's 

 great monograph, it is likely that his study of this structure was 



