SPONGIA OFFICINALIS. 



sprouting as it were from the albuminous crust which coats 

 the skeleton, without the appearance of any organs appropri- 

 ated to their development. As they increase in size, they are 

 found to project more and more into the canals which ramify 

 through the sponge, and to be provided with an apparatus of 

 locomotion of a description which will be frequently noticed. 

 The gemmule assumes an ovoid form, Plate I. Fig. 2, B, 

 and a large portion of its surface becomes covered with innu- 

 merable vibrating hairs or cilia, as they are denominated, 

 which are of inconceivable minuteness, yet individually capa- 

 ble of exercising rapid movements which produce currents in 

 the surrounding fluid. As soon, therefore, as a gemmule is 

 sufficiently mature, it becomes detached from the nidus where 

 it was formed, and, whirled along by the issuing streams 

 which are expelled through the fecal orifices of the parent, it 

 escapes into the water around. Instead, however, of falling 

 to the bottom, as so apparently helpless a particle of jelly 

 might be expected to do, the ceaseless vibration of the cilia 

 upon its surface propels it rapidly along, until, being removed 

 to a considerable distance from its original, it attaches itself 

 to a proper object, and, losing the locomotive cilia which it al 

 first possessed, becomes fixed and motionless, and develops 

 within its substance the skeleton peculiar to its species, ex- 

 hibiting by degrees the form of the individual from which il 

 sprung. It is curious to observe the remarkable exception 

 which sponges exhibit to the usual phenomena witnessed in 

 the reproduction of animals, the object of which is evident, as 

 the result is admirable. The parent sponge, deprived of all 

 power of movement, would obviously be incapable of dispers- 

 ing to a distance the numerous progeny which it furnishes', 

 they must inevitably have accumulated in the immediate vi- 

 cinity of their place of birth, without the possibility of their 

 distribution to other localities. The seeds of vegetables, 

 sometimes winged and plumed for the purpose, are blown 

 about by the winds, or transported by various agencies to dis- 

 tant places ; but in the present instance, the still waters in 

 which sponges grow would not have served to transport their 

 progeny elsewhere, and germs so soft and delicate could 

 hardly be removed by other creatures. Instead, therefore, of 

 being helpless at their birth, the young sponges can, by means 

 of their cilia, row themselves about at pleasure, and enjoy for 

 a period powers of locomotion denied to their adult state. 



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