OCR Text |
Show 154 DR. II. LYSTER JAMESON ON THE [Mar. 4, connective tissue of the mantle-margin, where it is attached to the "pallial line," especially along the ventral border, and around the insertion of the siphonal musculature. The favourite place seems to be the dorsal side of the latter. The individual Sporocysts are embedded in and closely adherent to the bundles of muscle-fibres. In young examples I found small, simple, spherical or oval Sporocysts, about *5 m m . in diameter, and containing 6-10 Cercariae, but in larger examples groups of Sporocysts occur (PL X V I . fig. 9, and text-fig. 24). Text-fig. 24. Tapes decussatus. Group of Secondary Sporocysts, as seen in a pressure preparation. m.t., muscular tissue of Tapes ; sp.c, Sporocyst; cer., Cercaria contained in Sporocyst. The individual Sporocysts in these cases are often larger than the simple ones. The groups are, from their position, their relations to one another, and their progressive increase in size and number of constituent cysts as Tapes grows older, evidently produced by budding or secondary division of the original simple ones. Their growth is very slow, and their duration of life must be practically co-extensive with that of their host. In large specimens of Tapes they appear to represent several successive infections; as we may have, in the same individual, large groups, probably several years old, smaller ones containing three or four cysts, and finally little single Sporocysts like those found in young individuals. On the other hand, in young Tapes, 10-20 m m. long, although the simple cysts and small groups occur, the large groups are not to be found. Specimens of Tapes measuring 12 x 10 mm., with one marked period or interruption in the growth-rings on the shell, contained |