LEPTOMKIH'S.-E — PHIALIDIUM. 271 



relatively fewer lithocysts than in P. hemisphcericum. Stomach much larger than in P. hemi- 

 spharicum. There are 4 straight, narrow radial-canals with 4 short, swollen gonads on their 

 distal outer parts. These gonads are shorter and more swollen than in P. kemispheericurh. 



The green color of the stomach is very characteristic. The gonads and tentacle-bulbs 

 dull yellow. Found in the Mediterranean. I have seen this medusa at Naples. 



Metschnikoff studied the early stages of development of this medusa and the following 

 is a brief abstract of his results: 



The egg is 0.16 mm. wide and laid at 8 in the evening in March and April. Segmentation 

 is total and almost equal. A one-layered, ciliated, spindle-shaped larva is formed and the 

 entoderm is produced by cells which migrate into the segmentation cavity from its narrow 

 hinder end. Then it attaches itself by its forward end and the hinder end grows upward into 

 a hydroid. Unfortunately we know nothing of the full-grown hydroid, and it will be impossible 

 to determine the various species of Phialidium with certainty until we acquire a fuller know- 

 ledge of their hydroid stocks. 



Phialidium mccradyi. 



Plate 34, figs. 2, 3; plate 35, figs. 1-3. 



Epenthesis mccradyi, Brooks, 1888, Johns Hopkins Univ. Circulars, vol. 7, No. 63, pp. 29-30; 1888, Studies Johns Hopkins 

 University Biol. Lab., vol. 4, pp. 147-162, plates 13-15. — Sigerfoos, 1893, Johns Hopkins Univ. Circ., vol. 12, No. 106, 

 p. 106. 



Oceania mccradyi, Mayer, 1900, Bull. Mus. Comp. Zool. at Harvard College, vol. 37, p. 5°. P late z >' fi S s - 5 6 "59; '9°4> Mem - 

 Brooklyn Inst. Museum Nat. Sci., vol. 1, p. 15, plate 3, figs. 23, 24. 



Bell very flexible and of soft consistency; about 15 mm. in diameter and shallow, about 

 twice as broad as high. The tentacles vary in number from about 16 to about 24. There are 

 1 to 2 lithocysts between each successive pair of tentacles. Each lithocyst contains a single 

 spherical concretion. Velum well developed. There are 4 straight, narrow radial tubes and 

 a slender, circular vessel. The small, swollen gonads are found upon the radial tubes about 

 midway between margin of bell and manubrium. Serial sections of gonads have been studied 

 by Brooks, 1888, Sigerfoos, 1893, and ourselves. The most careful study of their early stages 

 has been made by Sigerfoos, while Brooks has presented good figures of their later conditions 

 (see Brooks, 1888, Studies Johns Hopkins Univ. Biol. Lab., vol. 4, plate 15). It appears that 

 the gonads may develop in one of two ways. They may develop into simple reproductive 

 organs containing either male or female cells, or they may develop hydroid blastostyles 

 which in turn give rise to free-swimming medusae. According to Sigerfoos, if the latter is their 

 destination, the following changes take place: The young reproductive organ consists of a 

 layer of small ectodermal cells covering it externally, and a layer of larger entodermal cells 

 lining it internally. As the organ grows the ectoderm becomes much thicker and many- 

 layered by the multiplication of its cells. At the same time the cells of the entoderm enlarge 

 and become vacuolated, but still remain in a single layer. Before the organ has matured, 

 however, the outer layer of ectodermal cells becomes separated off from the remaining ecto- 

 derm by the appearance of a supporting lamella between them. At this stage, then, the organ 

 consists of a single layer of small ectoderm cells covering it externally, and a single layer of 

 large, vacuolated, entodermal cells lining it internally; between the two is the thick middle 

 mass'of cells of ectodermal origin. Evaginations of the entodermal lining then push out into the 

 middle layer as finger-shaped processes. While this is taking place the entodermal cells ot 

 these processes undergo marked changes. They decrease very muchin sizeandlosetheirvacuo- 

 lated character. They then lose their connection with the entodermal lining of the gonad 

 and become closed cylindrical tubes of entodermal cells lying within the middle mass of ecto- 

 derm-cells. The ectoderm of the bud is formed from the single layer of superficial ectoderm 

 cells that overlies the gonad. Thus the bud is formed from both ectoderm and entoderm. 

 When set free the young medusas have 8 marginal tentacles, alternating with 8 lithocysts. 

 The manubrium of the mature medusa is short and stout, and there are 4 recurved lips. 



The entodermal lamella of the bell and the entoderm of the basal bulbs of the tentacles 

 are of a delicate pink color. The entoderm of the gonads, of the manubrium, and of the bud- 

 ding medusae is green. There are 4 interradial, longitudinal bands of dark-green entodermal 

 pigment-spots upon stomach, and also a number of the same kind of spots upon gonads. 



