IT is well known that the Oligochaeta (like many other animals such as molluscs, insects, c they are sometimes even slightly imbedded in the skin. The other type of spermatophore characterises Tubifex and several allied genera, as well as the Eudrilid earthworm, Polytoreutus. These are long thin motile bodies. They are found only in the spermathecae of those Annelids which they characterise. I have lately studied the structure of a third variety of spermatophore which I found in the spermathecal sac of another Eudrilid genus, Stuhlmannia. This worm is long and slender, not measuring more than 2 mm. in diameter. The spermathecal sac in which the spermatophores are found is about 7 or 8 mm. long. I never found more than two of the spermatophores in a sac; they measure some 3 mm. in length. The shape is peculiar. There is a “head” very similar to that of the spermatophore of Tubifex, a long “beak,” open at the extremity, is followed by a circumferential swelling, which is again succeeded by a narrow neck; this in its turn gradually widens until at the middle the spermatophore is large and plump. The interior was a mass of separate spermatozoa entirely uncompacted together. The site of the formation of the spermatophores has been much disputed. It seems to be clear, from the investigations of Mr. Lankester, that in Tubifex they are at least moulded in the spermatheca, since the collar of the head of the spermatophore not only corresponded in form with certain foldings of the spermathecal wall, but was actually observed lying in situ. As to the origin of the material, Mr. Lankester and Prof. Vejdovsky were disposed to trace it, partly at least, to the “cement gland” of the male efferent apparatus. I find in Stuhlmannia that the moulding of the head of the spermatophore must be accomplished in the spermathecal sac, since I also observed a spermatophore lying in situ with its convexities fitting into corresponding concavities of the walls of that sac. Further, the large size of the spermatophore necessitates the hypothesis that the whole of it is moulded in the sac, since it could not possibly be contained—even with the greatest stretching—in the spermiducal gland. As to the origin of the material of the case, I hold it to be proved that part comes from the spermiducal gland and that the rest is, in all probability, a result of the breaking down of the abundant cells which line the spermathecal sac. I may add that no spermatozoa protrude through the case. This spermatophore of Stuhlmannia is evidently somewhat intermediate in its characters between the two types already known.