132 



THE MICROSCOPE AND ITS REVELATIONS. 



entire in the Zoophyte-trough. There are few parts of the coast on 

 which they may not be found, especially on a calm warm day, by skim- 

 ming the surface of the sea with the Tow-net ( 217); and they are capa- 

 ble of being stained and preserved in cells, after being hardened by osmic 

 acid. 



523. The history of the large and highly-developed Medusae, or ACA- 

 H^ which are commonly known as 'jelly-fish/ is essentially similar; 



FIG. 359. 



for their progeny have been ascertained to develop themselves in the first 

 instance under the Polype-form, and to lead a life which in all essential 

 respects is zoophytic; their development into Medusae taking place only 

 in the closing phase of their existence, and then rather by gemmation 

 from the original polype, than by a metamorphosis of its own fabric. 

 The huge Rhizostoma found commonly swimming round our coasts, and 

 the beautiful Chrysaora remarkable for its long 'furbelows' which act as 

 organs of prehension, are Oceanic Acalephs developed from very small 

 polypi tes, which fix themselves by a basal cup or disk. The embryo 

 emerges from the cavity of its parent, within which the first stages of its 

 development have taken place, in the condition of a ciliated 'gemmule,' 



of rather oblong form, very closely re- 

 sembling an Infusory Animalcule, but 

 destitute of a mouth. One end soon 

 contracts and attaches itself, however, 

 so as to form a foot; the other enlarges 

 and opens to form a mouth, four tuber- 

 cles sprouting around it, which grow 

 into tentacles; whilst the central cells 

 melt-down to form the cavity of the 

 stomach. Thus a Hydra-like polype is 

 formed, which soon acquires many addi- 

 tional tentacles; and this, according to 

 the observations of Sir J. G. Dalyell on 

 the Hydra tuba, which is the polype- 

 stage of the Chrysaora, leads in every 

 important particular the life of a 

 Hydra; propagates like it by repeated 

 gemmation, so that whole colonies are 

 formed as offsets from a single stock; 

 and can be multiplied like it by artifi- 

 cial division, each segment developing 

 itself into a perfect Hydra. There 

 seems to be no definite limit to its con- 

 tinuance in this state, or to its power 

 of giving origin to new polype-buds; 

 but when the time comes for the devel- 

 opment of its sexual gonozooids, the 



Successive stages A, B, c, D, of devel- *, . , . . 9 , . , . 



opment of Chrysaora: a, elongated and polype quits its Original Condition of a 



K H Txn'f> dcmrlav r*mfiinlpc (T?\cr 

 bell Wltn Blendei tentacles IJJ Ig. 



constricted Polype-body; 6, its original cir- 

 cle of tentacles; c, its secondary circle of 

 tentacles: d, proboscis of most advanced 359, C, a), assumes a cylindrical form, 



* P olype - bud from side of and elongates itself considerably; a 

 constriction or indentation is then seen 

 around it, just below the ring which encircles the mouth and gives origin 

 to the tentacles; and similar constrictions are soon repeated round the 

 lower parts of the cylinder, so as to give to the whole body somewhat the 

 appearance of a rouleau of coins (Fig. 359, A); a sort of fleshy bulb, a, 



