MUSEUM OF COMPARATIVE ZOOLOGY. 21 



There can be little doubt that the basement membrane is a product 

 of the hypodermis. There is a direct relation between its thickness and 

 that of the latter ; hence it is thickest on the dorsal, and thinnest on 

 the ventral surface of the animal. It is true that the hypodermis is 

 easily separated from the membrane, but on the other hand the intimate 

 relation between the two structures is evident from the manner in which 

 the cells of the former remain attached to the latter after the rhabditi 

 have been removed by partial maceration (Fig. 3) ; and even when 

 the hypodermis has been entirely removed, the outer contour of the 

 membrane in regions where, in consequence of the presence of many 

 rhabditi, the hypodermal cells have become much compressed, appears 

 irregular, the uneven projections representing the points of attachment 

 of the hypodermal cells. In those regions where the rhabditi are few 

 or absent, the basement membrane presents a comparatively smooth 

 surface. There is no evidence in Phagocata that the membrane is an 

 independent cellular tissue, as in Polyclads, since no traces of structure 

 could be demonstrated, the membrane appearing homogeneous with all 

 of the stains that were employed. In my opinion, therefore, the base- 

 ment membrane is of hypodermal origin. 



The pigmeyit in Phagocata occurs in the form of fine granules, of an 

 irregular outline and of a dirty greenish color. It lies principally in 

 the longitudinal bands of muscles between the fibres, so that, when a 

 worm is put under pressure and viewed with moderate powers, the 

 pigment appears as if arranged in parallel rows running lengthwise of 

 the animal. In the deeper tissues, below the muscle bands, the pigment 

 occurs in patches and streaks (Fig. 1). No pigment occurs normally 

 in the hypodermis. There are no special pigment cells ; the pigment 

 occurs in the form of distinct separate granules, which are intercellu- 

 lar in position, never intracellular. The origin of pigment as isolated 

 granules might be explained by some such theory as that of Eisig ('87, 

 p. 765), by which it is to be considered as a product of the excretory 

 system, — a kind of utilized excreta. 



There are only three systems of muscles: the circular, the longitudinal, 

 and the sagittal or dorso-ventral. As compared with the complicated 

 musculature of other fresh-water planarians, that of Phagocata is much 

 simplified, and in this respect it agrees with Gunda sementata (Lang, 

 '81 a , p. 193) and Planaria abscissa (Iijima, '87, p. 344). The circular 

 muscles form a single layer immediately under the basement membrane, 

 to which, as we have seen, they are closely applied. The longitudinal 

 muscles form a thick band inside of the circular layer, and are much 



