A CONTRIBUTION TO THE ANNELIDA. 55 
Spinther; indeed, none of von Graff’s figures indicate it, and 
no allusion thereto occurs in his description. 
Caruncle.—In horizontal section this highly sensitive 
tongue-shaped organ presents externally a thin layer of cuticle, 
the greater part of the area internally being formed of hypo-. 
dermic cells and granules. Posteriorly, in the middle line, 
however, is a double fibrous band, with at intervals various 
lateral fibres, which extend not only into the lateral regions 
but also into the narrow spaces between the bands. About 
the middle of the organ one band becomes prominent and its 
fibres spread more and more outward on each side until the 
eyes are reached. These fibres are probably contractile. In 
such a section as in Pl. 1, fig. 1, the pennate arrangement of 
the median fibres is conspicuous, and they merge laterally into 
the hypoderm. Moreover, in this section the complex mus- 
cular fibres which intercross at the margins, and which appa- 
rently are connected with the flattening of the organ, and other 
changes in its outline are clearly shown. 
In vertical section (PI. 6, fig. 2) the caruncle has a more or 
less radiate appearance, due to the fibres which diverge from 
the inferior area into the surrounding cellular stroma of the 
hypoderm. The area referred to increases in size from behind . 
forward, and in many views has a definite boundary or arch of 
decussating fibres superiorly. It (that is, the space below the 
arch) is occupied by a series of vertical fibres which radiate 
superiorly into the substance of the caruncle, and cause the 
somewhat arborescent appearance of the organ in section. 
While, therefore, the lower fibres in the area just mentioned 
are vertical, the upper are less definitely so. On the other 
hand, the fibres are almost wholly vertical in the small or un- 
developed condition of the area posteriorly, since they pass 
straight upward to diverge into the tissue of the caruncle. 
Below the latter the muscular fibres form a powerful band, 
which by-and-by are interlaced with longitudinal fibres in con- 
spicuous meshes (Pl. 6, figs. 2 and 3). The origin of these 
fibres would appear to be the raphe above the folds of the 
mouth. The area diminishes anteriorly, and seems to be occu- 
