54 



MEDUSAE OF THE WORLD. 



dermal core of the tentacle is hollow, and its lumen is continuous with the gastrovascular 

 system of the medusa. The ectodermal cells of the tentacle-bulb are very thick and are 

 probably nervous in function. The velum is well developed, being wide and thin. There 

 are 4 straight, slender radial-canals, and a simple, narrow, circular tube. A short, blindly- 

 ending tube extends upward from the base of the stomach into the gelatinous substance of the 

 bell. The entodermal cells of this small projection are several layers thick. The manubnum 

 is long and extends far beyond the velar opening. Its proximal part is slender and tubular, 

 but in its outer parts it is much distended by the genital products and consists of a long, 

 wide, cylindrical tube. The line of demarcation between the narrow and the wide part of 

 the manubrium is very sharp. The mouth is a simple opening at the extremity of a short 

 flask-shaped proboscis, and the lips are studded with nematocysts. The mature genital pro- 

 ducts are found in the ectoderm of the distal part of the manubrium. The entoderm of 

 the manubrium is usually green, but occasionally it is red. The entoderm of the tentacle- 

 bulbs is either red or green, and in some individuals the entoderm of the bulb is red while 

 the ectoderm is green. 



FIG. 16. "Syncoryne pulchella." 



FIG. 17. "Syncoryne frutescens." 



The above figures are after Allman, in Ray Society, 1871-72. 



Hydroid and young medusa. The hydroid stock is Syncoryne mirabilis. The stems 

 are attached by a creeping stolon. They are about 15 millimeters in height and branch 

 profusely. The main stems and also the side branches terminate each in a single polypite. 

 The stems are incased in an unannulated chitinous perisarc, which terminates sharply at 

 the bases of the polypites. Each polypite is fusiform and has about 12 to 18 tentacles which 

 arise in 3 or more indefinite whorls from the sides of the polypite. These tentacles are not 

 long, but are quite contractile. Each terminates in a knob-shaped cluster of nematocyst- 

 cells. The mouth of the polypite is a simple round opening situated at the extremity of a 

 conical proboscis. Medusa-buds are developed upon the sides of the polypites immediately 

 below the tentacles, near the lower base of the polypite. Each polypite bears I to 4 

 medusa-buds in various stages of development. In Massachusetts Bay the breeding season 

 begins early in March and lasts until the end of May. During March the medusa-buds 



