a peculiar construction, and to such cestodes the illustrious parasitologist Rudolphi applied the generic title of Rhyncobothrium. These rhyncobothria are now known to be mature tapeworms, whose larvæ had been previously regarded as distinct species under the generic title of Tetrarhynchus. For simplicity's sake we retain the latter title in place of the former, having already employed this title when describing a remarkable example of sexually immature tetrarhynchus in former pages of the INTELLECTUAL OBSERVER (vol. 2, p. 82). We shall also make use of Prof. Van Beneden's term "scolex" to specialise those larvæ, the heads of which resemble those of the adult or parent form. These scolices, then, are merely larval tape-worms, those belonging to the genus tetrarhynchus being particularly abundant in marine fishes, such as the cod, haddock, turbot, sole, and flounder; they are likewise found in the mackerel, mullet, gurnard, conger, sun-fish, and even, according to Von Siebold, in the cephalopodous molluscs or cuttlefishes.

The accompanying plate illustration represents a scolex of tetrarhynchus removed from the wall of the intestine of a common haddock. It was associated with several other larvæ of the same kind, varying in size from a pin's head to that of a pea. Each young tetrarhynch was enclosed in a thick-walled sac, such as is displayed in figs. 1 and 2, the latter representing the sac burst open, and magnified four diameters linear. Fig. 3 gives a general view of the scolex, which is inverted and enclosed within the bladder-like vesicle-the latter being, in point of fact, the tail. The four long filamentary proboscides are also seen here, and also the little highly-refracting dots, which represent what are termed "calcareous corpuscles.' The transverse lines are caused by the regular folding of the vesicles. Fig. 4 shows the head and neck of the natural size, everted. Fig. 5 is another view of the anterior end of the same, amplified about twenty diameters. It exhibits four narrow, pointed, sucking appendages, at the base of each of which is an open papilla, giving passage to one of the retractile proboscides or tentacles. These organs are armed with a complicated series of spines or hooks, but whilst lodged within the neck are embraced by a strong tubular and muscular sheath, which at the lower part is club-shaped, so as to form what has been termed the "lemniscus ;" the figure (5) also shows a portion of the large caudal vesicle, with the calcareous corpuscles in sitû. Fig. 5e represents a small portion of the wall of the neck, displaying a fine network of capillary tubes beneath the skin (x 260 diam.). Fig. 6 is an isolated sclerous or calcareous particle greatly enlarged; fig. 7 being a section of one of the retractile proboscides, showing the relative size and disposition