"MEDUSA DUOPECILIA." 69 



" As in some other Medusae, the ciUary or tentacular organs resemble knotted cords. 

 Each pair originate from a prominent knob or button on the margin of the cavity in the 

 under part ; and a black speck, like an eye, is conspicuous at the root of each tentaculura : 

 there are, therefore, eight in all. The transparent convex surface of the animal is crossed by 

 two darker lines at right angles, as if dividing it into quarters, and terminating in the four 

 buttons or knobs on the margin. 



" The opacity of this creature, during its earher stages, is not such as entirely to intercept 

 the light, though its transparence refines in proportion to the evolution of its organization. 

 Thus, the cross lines running from what was conjectured an orifice are discovered to be four 

 vessels, wherein a fluid carries a number of black particles down to the marginal knobs below. 

 It rather appears also, though I could not satisfy myself of the fact, that the current may pass 

 in another course around the margin. 



" We should be much deluded, as well as our fellows, in believing that sufficient oppor- 

 tunities are afforded for similar observations by the Medusa free of the zoophyte, and swimming 

 at large. On the contrary, they can be effected only while immaturity yet restrains the 

 animal to its pristine site ; and where, during progressive evolution, the microscopical focus 

 can be accurately adjusted for distinct vision. The motion of so restless a being, when 

 liberated, renders correct observation incompatible with that condition. 



" One of the pyrula seemed to be united to a hydra, just at the orifice of the twig from 

 which it issued. Circulation manifestly advanced in both. Black particles were carried up as 

 well as down the neck of the former, the p3rrulum, and during their descent, a current was 

 obviously conveying black particles up the body of the hydra ; something similar seemed to 

 be going on in an isolated pyrulum, where there was no hydra. 



* * « » * JyS * - 



"The preceding animals originated and disappeared without leaving any traces behind. 

 Indeed the smaller Medusae never leave anything that I have seen. 



" Another species {Medusa duodecilia) has sometimes appeared and decayed mysteriously, 

 without affording obvious indications of its origin. This animal occurs in April ; the former is 

 developed from June until August. It is an eighth of an inch in diameter, with sixteen long, 

 slender, tentacular, or ciliary organs, disposed in four bundles, which issue from four marginal 

 prominences. At the base of each set is a black speck. The transparence of the Medusa is 

 such, that while suspended in equilibrium in the water it is scarcely perceptible. 



" The evolution of the Medusa ocilia is progressive, accelerated perhaps by external 

 temperature. It has occurred to me under no other conditions than as above specified. A 

 number of whitish corpuscula seem to be generated rather suddenly among the hydrae, either 

 singly, in pairs, or in clusters of three, four, or five, as already stated. Each is affixed by an 

 independent pedicle, and generally about the orifice of a twig of the zoophyte. One, wherein 

 no subordinate organic parts were visible, on first inspection, was observed to unfold in three 

 hours. 



" There is reason to believe that this Medusa is confined ka. a diaphanous vesicle or 

 involucrum, remaining in its place after the animal has escaped. If actually so, which requires 

 confirmation, we cannot but recognise strict analogy to the vesicles of the Sertularia, some 

 being hardly perceptible after discharging their contents, from extreme transparency. 



" A colony, computed at 130 individuals, of the Medusa ocilia was produced in four or 



