66 collinge: on the anatomy of the vitrina irradians. 



rcceptaculum scminis, and the free-oviduct. The latter is of consider- 

 able length, and just beyond its middle it expands and forms a 

 thick-walled cavity, beyond which it is continued as a tube. The 

 whole of its internal walls are richly plicated, the plicae taking various 

 forms as shown in Fig. 3. The penis is a large, muscular organ with 

 a diverticulum. Its internal structure is very interesting, and presents 

 many points difficult of interpretation. Commencing at the vestibule 

 as a fairly uniform tube, it expands distally into a somewhat bulbous 

 head, beyond which is the diverticulum, a blindly ending tube, while 

 to the left side is an epiphallus,* somewhat S-shaped, and tube-like 

 at first, but becoming more globose at the point where it meets with 

 the vas deferens. In one, the largest, of the seven specimens 

 dissected, the epiphallus exhibited the form shown in Fig. 6. When 

 dissected (Fig. 4) a thick, muscular penis-sheath is seen, whose 

 internal walls are studded with numerous, minute, fleshy, knob-like 

 processes, enclosed by this sheath is the evertible penis (Figs. 4 and 5), 

 which is also covered with fleshy, knob-like processes. It has a 

 narrow neck, expanding terminally into a globular head, while passing 

 through the whole of its length is a fine canal. The diverticulum is 

 a hollow, blindly ending sac, with smooth, muscular walls ; as it 

 reaches the evertible penis the lumen of the cavity narrows and 

 becomes continuous with the canal passing through the penis 

 (Fig. 4, div.). The epiphallus has also richly plicated walls for part 

 of its length, the plicae being somewhat moniliform ; the walls of the 

 last bend, the kalk-sac, are almost smooth and the cavity is filled 

 with a mass of minute, white, calcareous granules, while from the 

 base of the cavity, in the two largest specimens, a long, hollow spicule, 

 measuring about 6*5 millim., in length, arises. (Fig. 7). At first 

 sight, this body reminds one of a dart, for basally it expands shghtly, 

 and is firmly implanted in the muscular tissue at the base of the sac. 

 Clustered around it are large numbers of the white, calcareous 

 granules. When examined under the microscope, these granules are 

 seen to vary greatly in size, shape, and composition, and seem to be 

 most numerous in fully matured animals. The largest are biconvex 

 (Fig. 6a) and when viewed under a high power (yVth water immersion), 

 they are seen to contain certain definite contents (Fig. 6a); still more 

 numerous are smaller oval granules (Fig. 6^), while a few perfectly 

 spherical granules, of various sizes, are also present (Fig. 6r). When 

 pressure was brought to bear upon the cover glass, the large biconvex 



111 specimens measuring 36 to 50 millim. this organ was very short. 



