DR M'INTOSH ON SOME POINTS IN THE STRUCTURE OF TUBIFEX. 259 



fluid, and, as has long been supposed, doubtless performs important functions 

 in the animal economy; as, indeed, the observations of Frey and Leuckart, De 

 Quatrefages, and Dr Williams, show it does in other invertebrate animals. 

 I think, however, that too little attention has been bestowed upon the in- 

 herent properties of the fluid itself. Perhaps the remarkable corpuscles 

 contained therein are the products of such inherent properties, and not 

 necessarily derived from its surroundings. If the glands covering the intestine 

 discharge their contents into the perivisceral fluid, as most authors believe, such 

 a discharge probably only furnishes materials for the evolution of the special 

 properties of the liquid. It is well to bear in mind, also, that in the clearly 

 defined group of the Nemerteans, a fluid identical in appearance, coagulable 

 nature, and in the presence of definite corpuscles, occurs within . a special 

 muscular sheath on the dorsum of the intestine. This chamber has smooth 

 walls, and contains, besides, the proboscis, which, as it were, is invaginated 

 within it. The glandular elements, which exist in vast numbers in the walls of 

 the digestive tract, cannot thus communicate directly with the fluid. 



In the perivisceral space of one example was a curious parasitic larva 

 (Plate X. fig. 2) which moved backwards and forwards in its chamber. It 

 lengthened its body into the shape shown at a, then contracted itself as in b, 

 forming a club with a large rounded head, and finally assumed the appearance 

 figured at c; after which it again elongated itself and repeated the same con- 

 tractions. Its structure was minutely granular, with a streak at the anterior 

 end. It appears to be the same form as that described subsequently from the 

 lobule of the testis (p. 265). 



Digestive System. — Granular Glands. — Anteriorly there are some finely 

 granular glands at the sides of the oesophagus ; and by-and-by numerous larger 

 glands cover the entire external surface of the alimentary canal, and envelope 

 the dorsal blood-vessel. These are somewhat pedicled structures, consisting of 

 a fine external membrane containing numerous distinct granules of an orange 

 or pale brownish hue (Plate X. figs. 3 and 4). When these bodies are extruded 

 into the water, the contained granules show very evident molecular movements, 

 and in a short time escape by the bursting of the cell- wall, their movements con- 

 tinuing in the surrounding fluid. The yellowish granules also occasionally 

 group themselves together, and larger granules are formed here and there, ap- 

 parently by the union of several. All the granules refract the light very strongly. 

 The gland-cells are rendered more translucent by acetic acid, which, however, 

 does not affect the granules. On the addition of sulphuric ether the residue 

 clearly shows that their composition is of a fatty nature. Dr Buchholz* is of 

 opinion that the pigment-granules of these cells in Lumbriculus variegatus is a 



* Beitrage zur Anat. der Gattung Enchytrceus, &c. Schriften der Physik. okonom. Gesellschaft 

 in Konigsberg, 1862, p. 108. 



