MUSEUM OF COMPARATIVE ZOOLOGY. 175 



cells is very difficult to prove in sections ; but in a badly preserved and 

 hence partially macerated preparation there was in many places a defi- 

 nite continuity of these cells with the fibres and underlying nuclei. 

 The probability of a direct continuity of the hypodermal cells with the 

 central nervous system through the anterior commissure seems to me to 

 be strong evidence in favor of the special sensory nature of the organ. 

 An examination of its morphological relations also yields much that is 

 favorable to this view. 



The existence of a glandular area, the direct connection of the organ 

 with the central nervous system, and its median position near the an- 

 terior extremity of the body, all point to its close relationship to such 

 sense organs as are cited by Dewoletzky ('87, p. 278), and as are com- 

 mon in the class Vermes. These have their origin, according to Dewo- 

 letzky, in " ein Paar flimmernder Hauteinstiilpungen." Whether the 

 same holds for this cerebral organ of Sipunculus can naturally be de- 

 cided only upon embryological evidence. Hatschek ('83, p. 115) says 

 that toward the close of the larval stage two " Wimpergruben " are 

 formed, one on either side of and near the median line. Further, he 

 says, " Es sind dies wohl Sinnesorgane die sich wahrscheinlich auch am 

 erwachsenen Thiere werden nachweisen lassen." These would by their 

 fusion produce an organ which, in position at least, would correspond 

 to that which I have described ; and from the absence of any other 

 structure to which these Wimpergruben can be traced, it is allowable 

 to assume their genetic connection with this cerebral organ until the 

 development shall furnish positive evidence on the question. That this 

 organ might be the apical area (Scheitelfeld) which, by the recession of 

 the brain from the surface, had come to be connected with the exterior 

 by means of a canal, is disproved by Hatschek's ('83, p. 108) observa- 

 tion that there is a complete separation of the ganglion from the body 

 wall at the time of its retreat ; according to the same author, the forma- 

 tion of the Wimpergruben was subsequent to this separation. 



If, now, the other members of the group of Sipunculids be examined 

 for similar structures, two cases are found which require consideration. 

 Shipley ('90, p. 18) has described an infolding of the preoral lobe which 

 extends to the surface of the brain, and from which a pair of retort- 

 shaped tubes penetrate into the ganglionic mass, one at each dorsal 

 lateral angle of the bram. The cells of the inner limb of the tubes 

 socrete a black pigment. Andrews ('90, p. 418) finds in S. Gouldii two 

 similar tubes proceeding from the lateral edges of a transverse pit an- 

 terior to the ridges of the ciliated cushion. These tubes extend into 



