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Rh ratus differs remarkably from that of the Nematoids, and I could remark no trace of movement in any individual,—all of which were females,—however fresh I examined them: the young ones, on the contrary, moved about in a lively manner. In this animal the interesting occurrence takes place, that the young are entirely unlike the full-grown animal, their skin being quite smooth, while that of the mother animal is studded with vesicular projections, giving to it a very pretty appearance."

The only other original notice of this extraordinary creature which I have met with is a note to Siebold and Stannius' "Anatomie comparée." They say:—

"On ne trouve ni bouche ni anus chez la Sphærularia Bombi, et le canal intestinal est remplacé par une série d'utricules allongées, adhereutes ensemble, et autour desquelles s'enroulent les organes genitaux."

Except that the series of large cells is double, instead of single, and that one end of the worm is easily distinguishable by the presence of the vulva, these statements are all, I believe, perfectly correct; they still, however, leave a great many points to be ascertained, and it was with a hope of supplying the deficiency that I undertook the subject. My good fortune has been smaller than my hopes; but, though the present memoir is lamentably incomplete, it may not, I hope, be found entirely without interest.

M. Léon Dufour and Von Siebold met with Sphærularia in the four species of humble bees—namely, Bombus terrestris, hortorum, sylvarum, and muscorum. I have found it in the females of B. terrestris, lucorum, pratorum, lapidarius, subterraneus, hortorum, and mus- corum, which increases to eight the number of species in which Sphærularia is known more or less frequently to reside. The proportion of specimens attacked is, however, very different in the different species, and the parasite appears to be most common in B. terrestris, lapidarius, and lucorum. Out of thirty-three specimens of B. terrestris examined by me in the months of May and June, no less than nineteen—that is to say, more than one-half—contained these parasites. The following table shows the number of bees examined, and the proportion which were affected:—

I have not had any opportunity of examining B. sylvarum; and it will be observed that B. muscorum and hortorum, in which the parasite was found by V. Siebold, have only supplied me with a single infected specimen each, out of twenty-nine which I examined.

Neither Léon Dufour nor Siebold say anything about the sex of