Prof. Allman on the Hydroida. 5 



structure can as yet be detected, to the completely formed ac- 

 tively contracting medusoid on the point of becoming free. 



I have been unable to demonstrate in the gonophores any 

 trace of an ectotheca. They are thus truly naked medusoids. 

 When arrived at that stage in which they detach themselves 

 from the stalk and become free, they present a deep umbrella 

 {nectocalyx, Huxley), becoming slightly narrower towards the 

 aperture, and having its summit continued into a short conical 

 projection traversed by a narrow canal which had kept the cavity 

 of the manubrium in communication with that of the stalk. 

 There are four radiating canals, each of which expands into a 

 bulb at the point where it enters the circular canal. Of these 

 bulbs one is much larger than any of the other three ; this bulb 

 is continued into a tentacle, while none of the others present 

 any trace of such an appendage : they all contain reddish-brown 

 pigment-granules ; and an obscure ocellus may generally be re- 

 cognized in a little accumulation of granules of a somewhat 

 redder colour situated beneath the ectoderm of the outer side of 

 the bulb. There is a broad velum. 



The solitary tentacle is largely developed, and consists of a 

 very extensile moniliform cord, presenting, when extended, the 

 appearance of ten or twelve little spherules distributed at equal 

 distances upon a cylindrical string : the last of these spherules 

 exactly terminates the string, and is larger than the others, 

 while one or two situated near the proximal end are smaller and 

 less distinct. The spherules are composed of accumulations of 

 thread-cells; and the connecting cord seems to have its axis 

 occupied by an uninterrupted tube directly prolonged from the 

 cavity of the bulb at its root. During contraction, the spherules 

 assume the form of circular disks ; and in extreme contraction, 

 the connecting cord disappears, and the surfaces of the disks 

 are brought into contact. 



The manubrium is large and subcylindrical, and the mouth is 

 without tentacula or lobes. 



From the above description it will be at once apparent that 

 the medusoid of Corymorpha nutans belongs to a form to which 

 Edward Forbes has given the generic name of Steenstrupia. Of 

 this relation between Steenstrupia and Corymorpha Forbes him- 

 self had a suspicion ; indeed, he expresses a belief that his Steen- 

 strupia rubra will turn out to be the free medusoid of Corymorpha 

 nutans. 



The medusoids, when they become free, are about -^ inch in 

 diameter, and as yet show no trace of generative elements ; and 

 though I kept them alive for more than a week, they scarcely 

 increased in size, and never showed any appearance of ova or 

 spermatozoa. 



