14 



thus metamorphosed into an animal, which, like the ( pla- 

 nula' of the Hydrozoa, typifies the ciliated infusorial Leu- 

 cophrys-, ciliated lobes, like those of a Rotifer, are next 

 developed from one extremity ; these grow into arms, and 

 the whole animal assumes the form of a polype : as such it 

 was originally described by Sir J. G. Daly ell, under the 

 name of Hydra Tuba, and in this state it propagates by 

 gemmation. 



The condition of this * Parthenogenesis,' or power of 

 propagation by the virgin larval polype, appears to reside, 

 as in the Hydra fusca, in the following structure : " The 

 body and tentacula of the larva are composed of two 

 distinct layers, an internal and external. The internal 

 layer chiefly consists of nuclei and nucleated cells of va- 

 rious sizes, some of them containing a large number of 

 nuclei ; while the external is chiefly composed of a struc- 

 tureless substance with numerous minute nuclei dissemi- 

 nated through it *." Sir J. G.' Dalyell obtained a colony 

 of eighty-three Hydrae Tuba, by buds, from one parent. 

 But the procreative force is not hereby exhausted. After 

 one, two or more years of captivity the body of the polype 

 has been observed to become thickened and impressed by 

 circular grooves : these, deepening, divide the outer surface 

 into rings, and this annulated part of the body may be sup- 

 ported on a contracted and smooth base ; the whole polype 

 being lengthened by the successive development of the seg- 

 ments so indicated : the margins of these segments next 

 shoot out short tentacles in eight pairs, and then the whole of 

 the annular partf is resolved by a series of spontaneous fis- 

 sions into as many small medusiform discs, which by growth 

 and a minor amount of metamorphosis are developed into 

 true Medusae. In certain of these individuals sperm-sacs 



* Dr. J. Reid's ' Observations on the Development of the Medusae.' 

 Taylor's Annals of Natural History, 1848, p. 26. 



\ The base may remain, reproduce the arms of the Hydra, and again 

 propagate by gemmation and spontaneous fission. 



