156 BULLETIN OF THE 



separated from it by a neck, the diameter of wbicli is slightly smaller than 

 the constriction in the dumb-bell shaped organ itself. The whole interior of 

 the end of the, tentacle is filled with patches of crimson pigment, which are. 

 enclosed in a layer formed of elongated cells placed side by side. Extend- 

 ing over this cell-layer is a second and thicker stratum, composed of smaller, 

 less regularly arranged cells. All these histological structures taken together 

 impai't to this portion of the tentacle the resemblance to a specialized sense 

 organ of some kind. The tentacle itself is composed of large central cells and 

 a thin layer of ectoderm. Its interior resembles that of a Cunina tentacle. 



Otocysts wanting. 



Development unknown. Single specimen was a female. 



Locality, Newport, R. I. 



Zygodactyla groenlandica, Agassiz. 



Plate V. Figs. 5, 6, 11, 18. 



These jelly-fishes are sometimes two or three inches more in diameter than 

 measurements which others have given. When fully extended, they are often- 

 times eighteen inches in diameter. They are very abundant at Newport in the 

 last of August. To the description which has been given of the adult can be 

 added, that, extending in radial rows from centre to circumference, between 

 each pair of radial tubes on the under side of the umbrella, there are rows of 

 small tubercles or simple knobs, prolongations of the substance of the disk. 

 There are about twenty such tubercles in each row. In the young Zygo- 

 dactyla with eight tubes, these tubercles were present, but limited to a circle 

 with a radius half that of the disk of the jelly-fish itself. I have not found 

 similar tubercles placed on the inner surface of the umbrella described in any 

 other medusa. In some cases, as often happens in a Zygodactyla, two of the 

 tubes divide in their course half-way between stomach and beU margin. The 

 lines of tubercles also bifurcate, and follow the tubes between which they lie. 

 On each side of the base of a single tentacle of Zygodactyla, there is a green 

 body, the function of which is not known. If the openings at the base of the 

 tentacle are, as has been suggested, depuratory orifices, these structures may 

 play some important part in this function. Plate V. fig. 11, taken from a 

 young Zygodactyla, where the tentacle is but slightly developed, shows both the 

 depuratory opening and the pair of green bodies adjacent to it. The very 

 young tentacle has at its tip lasso-cells, which disappear with age. The rela- 

 tive size of the green bodies also becomes reduced as the Zygodactyla grows 

 older. 



The jelly-fish represented in Fig. 156 of the "North American Acaleph{B"is 

 proljably not the young of this animal. It is too small, and has four genital 

 organs, one on each of but four chymiferous tubes. The development of other 

 tubes takes place before any sign of the genitals appears ; and when sexual 

 organs do develop, they do not begin as round bodies limited to one point on 



