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Show 19U1.J FROM BRITISH EAST AFRICA. 343 to be compared together. Up to the present these and P. violaceus are the only three species of the genus in which they have been discovered. I have re-examined P. gregorianus and P. finni in the hope of finding spermatophores, but quite in vain. The matter would be of obvious interest, since it is clear from the drawings exhibited that the two species with which I am concerned in the present communication can be amply discriminated by their spermatophores aloue. In P. magilensis they are all of the same form and vary only iu their length, which is in some cases (see text-fig. 85, p. 342) considerably in excess of the length which I originally figured. The spermatophore is extremely thin in proportion to its length, and is expanded invariably at one end into a spoon-shaped head. It dies away at the other end to a tine point. The body throughout is closely beset with a fine covering of spermatozoa, and I cannot but doubt that these spermatophores also are mobile during life. But they were not twisted into the tight coils so characteristic of those of P. hindei. The relative sizes and the differences in structure can be gathered from the sketches (text-figs. 84 & 85). In originally describing these spermatophores 1 commented upon their likeness to immature spermatophores in Tubifex, and thought that they might be in a state of immaturity. However, the occurrence of abundant spermatophores of precisely the same form in a second individual of the same species which I record here seems to me to do away with that possibility. Furthermore, there were no intermediate stages which would suggest a development of the theoretically immature spermatophores of P. magilensis into fully formed ones like those of P. hindei and P. violaceus. All the spermatophores-a very large number and, as I have already stated, from two individuals-were at precisely the same stage, which must be therefore, I should imagine, their definitive stage. Among the fully-formed spermatophores were a number (text-fig. 85, B ) which had lost their contents, and were simply empty sacs, more or less hyaline in character, and preserving the exact form of the uninjured spermatophore. This material was not suggestive of the granular matter figured by Vejdovsky in the immature spermatophore of Tubifex, which he ascertained to proceed from the secretion of the cement-gland or at least from the atrium of that worm. It appears to me, in fact, that the spermatophores of Polgtoreutus magilensis are really constructed on the same plan as those of the two other species of the genus in which they occur, but that the actual case of the spermatophore is much more slender and thus the spermatozoa project much further out. The result is an entirely different aspect, which is well shown in the drawings exhibited herewith. As to the spermatophores of Polgtoreutus violaceus aud P. hindei, their close likeness to those of theTubificidse other than Bothrioneuron is very striking and applies to details of structure. Very often, though not in every case, the anterior end of the spermatophore, which is sometimes slightly swollen, was distinctly opeu, as shown in the |