HYDRO-MEDUSA. 77 



cisely what occurs when the Ephyras of Aurelia separate, and 

 bear off the reproductive organs from the hydra-form. Yet, for 



the description of the male of this Hydroid. Fortunately for science, the sen- 

 tence beginning four lines below this was overlooked, and remains unaltered as a 

 crushing evidence against the wholesale assumption just above it. ***'' the 

 specimens died"***\l) I have given it as my opinion elsewhere, (Proceed- 

 ings Boston Society of Natural History, Dec. 2d, 1863,) that "the probable ex- 

 planation is that the medusoid " (meduso-genital) " withers, and becomes re- 

 sorbed, and then a hydroid head develops directly from the end of the old stem." 

 Coryne mirabilis. Ag. The other Hydroid which I propose to describe here is 

 known as Coryne, and is much more common than the first one, not only along our 

 coast, but even in the brackish waters at the mouths of rivers, at- 

 tached to rocks and floating timbers, &c. It varies in height and 

 breadth according to the age of the colony, but usually the whole 

 branching group is not more than half an inch high (fig. 40). The 

 upright stems ramify more or less, and the end of each branch bears 

 a club-shaped head (fig. 42, m to rf), which is covered by a compli- 

 cated spiral row of globe-tipped feelers (<) The reproductive organs 



o " 



( pr, pr 1 ) are attached to the head behind, or occasionally among the group of 

 feelers. During the earlier part of the breeding season these organs develop 

 into highly organized bodies (fig. r cr c* p bl 



40, b), and finally break loose from 

 the head of the hydra and swim 

 away in this form (fig. 40, a), when 

 it is known as the medusa. It 

 seems to have, for all intents and 

 purposes, a perfect organization of 

 its own, excepting that it exhibits 

 no trace of a reproductive organ. 

 When just set free it measures 

 about one sixteenth of an inch in diameter (fig. 40, a), but in process of time it 

 grows to a diameter of half an inch (fig. 41), and at that size it has fully de- 

 Fig. 40. Coryne mirabilis. Ag. Natural size. A group of hydro-medusa, 

 at the height of the breeding season ; b, the meduso-genitalia ; a, the same just 

 set free, in the act of swimming. Oric/inal. 



Fig. 41. Coryne mirabilis. Ag. A full-grown meduso-genital, natural size, 

 in the act of swimming with the tentacles (t) trailing in the wake ; bl, the gelat- 

 inous bell ; p, the proboscis projecting through the aperture of the bell ; c, c 1 , 

 the four longitudinal canals ; cr, the circular canal ; r, junction of c, c 1 , and cr. 

 Original. 



