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Show 694 MR. F. E. B E D D A R D ON N E W [Dec. 20, of the aquatic Oligochaeta and of Moniligaster is to be seen in the genus Eudrilus. But Moniligaster obviously comes much closer to the aquatic Oligochaeta than does Eudrilus in this particular. Communicating with this muscular penis is the atrium. I have already described and figured the structure of the atrium in Moniligaster barwelli, and have pointed out its close similarity to the atrium of the Lumbriculidae; the Tubificid Branchiura has an atrium which is also constructed upon the same plan. In Moniligaster bahamensis we have the same low and darkly staining columnar epithelium lining the lumen ; this is surrounded also by the same comparatively thick circular muscular layer; in M. bahamensis, as in M. barwelli, the outermost covering of the atrium is formed by oval groups of pear-shaped cells. I find, however, that in the species of Moniligaster with which the present paper deals, the ducts of these cells, which are simply filiform prolongations of their substance, pierce the muscular layer in bundles and evidently pour their secretion into the lumen of the atrium. These ducts were exceedingly conspicuous owing to their dark staining, an effect possibly due to the presence of abundant secreted granules. They were probably overlooked in Moniligaster barwelli, owing to their not being stained. I could find no peritoneal layer even of the thinnest round the atrium. Rosa has described a somewhat different structure for the " prostates " (atria) of Desmogaster. He has above all insisted upon the presence of a peritoneal layer investing the organ superficially. The minute structure is described in the followiug words:- " II lume interim e piccolissimo, appena -J^ del diametro ; esso e tappezzato da un epitelio cilindrico. Esternamente a questo la massa delle pareti e prevalentemente muscolare; nella parte piu centrale le fibre sono annulari; in tutto il resto sono longitudinali, disposte in fasci raggianti. Nella regione piu esterna questi fasci divergendo racchiudono fra di loro delle ghiandole pluricellulari piriformi che per lunghi condotti vanno a raggiungere il lume interno, m a queste ghiandole non arrivano alia parete esterna deila prostata perche i fasci muscolari, benche ridotti a sottili strischie, passano fra una ghiandola e 1' alta e si ricongiungono fra loro, formando spesso solo un sottile rivestimento attorno alia base di esse. E inoltre ben evidente un rivestimento esterno peritoneale che spesso nelle sezioni si vede staccato. La superficie delle prostate non e racemosa como nei Moniligaster, m a liscia o appena ondulata, ed ha lo stesso aspctto sericeo delle prostate degli Eudi-ilus." This description and the illustrative figure are suggestive rather of the penis than the atrium of Moniligaster, particularly with regard to the gland-cells imbedded among the muscles. It appears to m e to be possible that Desmogaster differs from Moniligaster in that the atrium is not specialized into two regions. The ovaries are in the xith segment, attached to the front wall of that segment, as is so usual; the oviducal funnels open opposite to them and appear to be particularly large; but the most remarkable feature of the female reproductive organs of this Annelid are |