150 BULLETIN OF THE 



animation of poorly preserved material. Several times it was observed 

 that delicate filaments, branching from some nerve fibre of the skin, pro- 

 ceeded to the hypodermis and penetrated apparently undifferentiated 

 cells ; certainly the distal surface of these cells bore no sensory hair or 

 bristle. But the exact manner of termination of the nerve filament 

 remained in doubt. 



b. Cutis. 



In placing a cutis in the list of the layers of the body wall, I am not 

 unaware that the two most recent publications on Sipunculus deny its 

 presence. As already mentioned, Vogt und Yung ('88) regard the entire 

 extra-muscular layer as hypodermal, while Andrews ('90) evidently dis- 

 credits the existence of a cutis by omitting the name altogether. What, 

 then, is the actual condition of affairs 1 In sections one finds (Figs. 4, 5) 

 between the hypodermis and the muscular layers a mass of gelatinous 

 tissue, traversed in all directions by fibres, and containing not only 

 glands of various sorts, but nerve fibres and pigment cells as well. 

 Thus, though varying greatly in thickness in different regions of the 

 body, it may properly be regarded, in the light of the characters men- 

 tioned, as a true cutis. The principal part of this layer is the connect- 

 ive-tissue jelly, homogeneous in its consistency and forming the matrix 

 in which the nerves and dermal bodies lie. It is traversed in all direc- 

 tions by a multitude of the finest connective-tissue fibrils, which anas- 

 tomose but rarely. Occasionally a minute nucleus can be observed in 

 the course of a fibre. Scattered nuclei of a larger size, connected with 

 nerve fibres or amoeboid cells, are not infrequent in this mass, and 

 have been erroneously regarded as belonging to the connective tissue. 

 Irregular amoeboid cells with but one nucleus and of a different refractive 

 index from the general mass are found, sometimes in considerable num- 

 bers, and are perhaps similar in nature to the leucocytes of the tentacles, 

 to be described later. 



c. Pigment Cells. 



Besides these elements one finds multinuclear cells of irregular out- 

 line more or less filled with granules of a highly refractive character. 

 These are the pigment cells, so characteristic of this group that they de- 

 serve special consideration. Andreae ('81, p. 209) has given almost the 

 only description of these peculiar structures. He represents the pig- 

 ment granules as closely packed in meshes of connective tissue on which 

 nuclei may be observed. This appearance is no doubt due to poorly 



