88 MICROSCOPICAL STUDIES. 



finger of a glove can be turned, and if we remember that the content 

 of the cyst is a watery fluid under considerable tension, one can 

 easily understand that if this tension be greatly and suddenly 

 intensified by pressure upon the walls from without, an instantaneous 

 throwing out of the ingrown hollow thread must ensue. 



A working model of such a cyst can be made of india-rubber 

 tissue, if fashioned in the form of a hollow bulb with the apex dwin- 

 dling down into a finger-shaped hollow appendix. If this hollow 

 model were partly filled with water and the filiform apex thrust 

 inwards (invaginated), then by squeezing the bulbous part, the 

 pressure of the contained water would force outwards the invaginated 

 finger the equivalent of the hollow filiform thread of the nematocyst. 

 In the Corynidae, the base of the thread is stout and furnished with 

 barbs. 



The stem of the tentacle is formed as in Obelia of a solid 

 core of vacuolated stiff-walled cells of endodermal origin, that act as 

 a supporting axis. The ectoderm is thin, but furnishes very delicate 

 yet powerful muscle elements that control the elongation and re- 

 traction of the tentacles. 



The mouth that is fed by these ministering and food-capturing 

 tentacles is small and terminal and difficult to distinguish, appearing 

 as a mere opening at the anterior end of the polypite. The large 

 cavity of the polypite is where digestion takes place, the endoderm 

 cells of this region secreting a fluid which rapidly dissolves the tissues 

 of the prey. Thence this nutrient fluid is passed along the hollow 

 ccenosarc to aid in the sustenance of the general body of the colony. 



Reproduction. Normally Syncoryne produces buds at various 

 and indefinite points scattered over the body of the polypite and 

 between the tentacles. These buds at first consist of a layer of 

 ectoderm covering a hollow button-like outgrowth of endoderm. Next 

 this endoderm projects four hollow radial processes which ultimately 

 become the four radial canals of the Medusa, into which the bud 

 eventually develops. At the same time a median outgrowth of 

 hollow endoderm, the future manubrium, grows down between the 

 four radial bands. 



With growth the form becomes distinctly bell-shaped, the 

 four marginal tentacles appear associated with the four radial canals, 

 and a pigmented eyespot ocellus develops at the base of each 

 tentacle. Thus, little by little, the bud changes into a well marked 

 medusiform organism connected to the polypite by a narrow neck. 

 At this stage the medusiform bud is usually nearly as large as the 

 polypite itself. At length, it begins to pulsate, to long for separate 

 and free existence, and its efforts quickly effect severance from the 

 mother polypite. 



