688 PROCEEDINGS OF THE ACADEMY OF [DeC. , 



methods, has been employed. The possibility remains that under 

 such treatment nerves and sensory cells may yet be demonstrated. 



The strongest evidence in favor of considering the lateral grooves 

 as sense organs is the fact that dermal sense organs — aside from 

 the well-known lateral sense organs ( " Seitenorgane" ) of the Pro- 

 tonemerteans, and the frontal organs of other forms — have lately 

 been discovered in certain Nemerteans. 



In the anterior part of the body of ParapoUa aurantiaca Coe^ 

 there occur paired structures, resembling the lateral grooves of 

 Zygeupolia, and in the same relative position — that is, in the sides 

 of the body posterior to the nephridia and anterior to the middle 

 intestine. Plate XLIV, fig. 03, represents a transverse section of 

 a part of the body wall of ParapoUa through one of the lateral 

 grooves. From this it may be seen that the outer longitudinal 

 muscle, just outside the lateral nerve chord, contains an abundance 

 of large swollen cutis gland cells, Ca. Gl..>. These cells stain blue 

 with hfematoxylin and are present only in the vicinity of the lat- 

 eral nerves, being absent from the rest of the cutis. The section 

 figured shows that the " lateral groove" is elevated above the 

 general surface level, but in other sections it is depressed into a 

 groove. 



This elevation and depression of the "groove" is interesting 

 when one recalls that, according to Burger (1895), the Protone- 

 mertean lateral sense organs and the Metanemerteau frontal organs 

 may be both invaginated and everted. ]N"o differentiated sense 

 cells or nerves are distinguishable in the " grooves " of ParapoUa. 



The length of the groove of ParapoUa is about the same as 

 that of ZijgeupoUa, and they are probably homologous structures. 



In the twelve dermal sense organs of the head, lately described 

 by me (1900 b) for Carinoma tremaphoros, although undoubted 

 sensory cells are present, only in one case could a nerve, running 

 to the pit, be demonstrated. 



The recent discovery of a pair of lateral sense organs in the 

 new Ileteronemertean Micrella rufa Puunett (1!)01 b) is of great 

 interest and value. Punnett describes " a lateral sense organ on 

 either side (fig. 2) shortly behind the excretory pore. In the pre- 



^ Dr. Coe has very kindly allowed me to exaiiine the slides of his tj'pe 

 specimen of ParapoUa and to make drawings of the sense organs. One of 

 these is shown on PI. XLIV, fig. 63. 



