Bibliographical Notices. 313 



colonies of minute transparent animals swimming in vessels of sea- 

 water, during the months of Fehruary, March and April. Their general 

 aspect very much resembled a flock of birds in distant flight, as re- 

 presented by landscape painters. After being transferred to vessels 

 free of other subjects, they continued several days in activity and 

 then disappeared. I could not account either for their origin or their 

 transience. They occurred only at rare intervals, and always iden- 

 tically under the same form." (p. 111.) These very minute beings, 

 for the expansion of an individual is only between one and two lines, 

 were evidently allied to the Medusae " both in configuration and in 

 habits," but they differed from the Medusae in the early date of their 

 appearance. To distinguish them Sir John called the species Me- 

 dusa bifida, and we have it minutely described and variously figured. 

 Sir John was first led to remark that it was chiefly observed in ves- 

 sels containing the Hydra tuba (p. 114) ; and subsequently, and as it 

 were by accident, he discovered that the hydra was in fact their 

 source ; and moreover that the hydra was identical with the Strobila 

 of Sars ! The discovery is told in a most interesting manner, and 

 with a truthfulness which there is no gainsaying. 



We shall quote only a few of the many passages we have marked, 

 previously observing that the Hydra tuba in its strobila-form is some- 

 thing like a fir-cone or a cylinder cut into several whorls, each whorl, 

 when detached, becoming what is named the Medusa bifida. The 

 strobila throws off these whorls in succession to the number of from 

 ten to twenty, when the basis, as already stated, reassumes the form 

 and habits of the hydra. 



" First, a smooth fleshy bulb sustained a cylinder of about half its 

 own diameter, indented by plain circles, which were soon converted 

 to waving curvatures. A row of twenty or twenty-four tentacula 

 crowned the summit of the cylinder, which row disappeared or was 

 obliterated as the waving in its vicinity deepened, and the diameter 

 of the cylinder there expanded, that is, towards the summit. Con- 

 comitant on obliteration of the terminal row, a new circle of tenta- 

 cula, at first few, but gradually augmenting, was emerging from 

 around the bulb, while the struggles of Medusae, into which the 

 waving strata were evolving, accomplished their liberation to swim 

 unconstrained in the surrounding element." (p. 121.) 



" Certain facts admit of no dispute ; such as the existence of a 

 vigorous hydra attached to a solid substance, with long flowing silky 

 tentacula ; an alteration in the figure of the body, or the formation of 

 an embryonic roll of Medusae on the disc ; the gradual maturity of 

 each Medusa and its liberation from the roll ; the disappearance of 

 the original tentacula of the hydra ; the emerging of a new circle 

 of tentacula from a smooth fleshy bulb, sustaining the embryonic 

 roll, as the former are obliterated, and as the Medusa? approach ma- 

 turity ; the evolution of thisfleshy bulb as a perfect hydra, along with 

 their departure, which becomes the parent of progeny by gemma- 

 tion, and its permanence as an independent animal." (p. 122-3.) 



" All the Medusae in the embryonic roll are separate and distinct 

 animals. Each is in close application to that which is next below, 

 if itself be uppermost, or lies between two if intermediate. The pro- 



Ann.fy Mag. N. Hist. Ser. 2. Vol. i, 21 



