Miscellaneous, 345 



This paper will deal briefly with the position, structure, and 

 nervous connexion of this organ in Yoldia. 



Two species have been studied — Y. limatula and T. sapotiUo. 

 Most of the material was obtained through Mr. Richard Eathbun, 

 of the U.S. Fish Commission, and Dr. James L. Kellogg, of Olivet 

 College. 



The siphons, long and slender in the adult animal, arise as ridges 

 at the mantle-margin, which ultimately unite in such a manner 

 that two closed tubes are formed. A muscle is developed which 

 serves to retract the siphons, and thus they may be completely 

 withdrawn between the mantle-lobes, although their bases originate 

 at the mantle-margins. 



The tentacle under discussion is attached to the point of union of 

 the ventral siphon with the adjacent mantle-lobe, on a level with 

 the vential border of this siphon, and it lies, when the siphons are 

 retracted, between the mantle-lobe to which it is attached on one 

 side and the walls of the siphons on the other. In both of the 

 species examined the tentacle occurs in about equal proportions on 

 the right and on the left sides, but is apparently never paired. 

 "When extended it is a long and slender filament, gradually tapering 

 to its free extremity, and set throughout its length with small some- 

 what conical papillte, at the tip of each of which ample magnifica- 

 tion shows a cluster of sense-hairs. When retracted it presents a 

 series of transverse wrinkles which tend to obscure these sense- 

 papillse. Beneath the surface-layer of epithelium run strands of 

 longitudinal muscle-fibres imbedded in connective tissue. On the 

 side nearest the mantle-lobe to which it is attached (right or left, 

 according to its position), and beneath the muscle-layer, is a large 

 nerve which can easily be traced to the tentacle's tip. On the side 

 opposite the nerve, also within the muscle-layer, is a more or less 

 definite space in the connective tissue which is likewise continuous 

 the length of the tentacle. This space, which appears to be a blood- 

 space, is best seen in cross-sections of a somewhat extended tentacle, 

 in which case remnants of a coagulum may be seen in it. Exten- 

 sion of the tentacle seems to be accomplished solely by forcing blood 

 into this space. When the muscles of the tentacle contract, the 

 blood is forced back, and the space may be completely obliterated. 



From the posterior end of each visceral ganglion a nerve arises 

 which soon divides. One of these divisions is distributed to the 

 siphons and their retractors, the other to the posterior portion of 

 the mantle-margin. It is from this latter division that the tentacle 

 receives its nerve. In specimens in which the siphons are strongly 

 retracted the base of the nerve which supplies the specialized tentacle 

 is pulled some distance above the tentacle's base. The two nerves, 

 which now lie side by side near the base of the tentacle, form a mass 

 of nervous matter which appears superficially much like a ganglion, 

 and doubtless has been mistaken for one. 



The posterior ventral margins of the mantle are fringed with 

 ordinary marginal tentacles which have, beneath the superficial 

 layer of epithelial cells, both longitudinal and transverse strands of 



