MICROSCOPICAL STUDIES. 37 



Once freed, it begins a long, free-swimming existence and rapidly 

 increases in size till it reaches fully |-in. in length. The manubrium 

 in this species attains enormous proportions — sometimes, when fully 

 extended, quite thrice the length of the bell. In this and allied forms 

 (i.e. among all the Gymnoblastic Hydroids), the genital organs 

 appear in the walls of the manubrium of the medusa. The sexes 

 are separate, and the embryos that are produced settle down and 

 develop hydroid stocks or colonies. 



I have said that the foregoing is the normal course of repro- 

 duction — but certain species, and among others that under present 

 consideration, S. eximia, have an alternative mode. This however 

 is practised only at the end of the breeding season (April) when the 

 reproductive buds, in place of developing into free medusa? (Sarsia, 

 as this form of medusa was called before it was recognised as one 

 stage in the life-cycle of this Hyclroid), remain permanently attached 

 to the hydroid stock. In form they have the same bell shape 

 as the true medusa-buds, but they seldom produce tentacles 

 (stunted when produced), and the manubrium becomes enormously 

 swollen with the reproductive products. The lack of tentacles is to 

 be adduced to the fact that owing to the permanence of attachment 

 to the parent, all nutritive matter is obtained from that source, and 

 the manubrium has no call to act as a digestive organ, but simply 

 as a reproductive gland. 



The next and final stage of degeneration is found in such forms 

 as constitute the genus Goryne, of which the lovely species G. 

 vaginata, grows luxuriantly in Jersey rock -pools and gullies — where 

 it forms elegant branched colonies that appear miniature shrubs, 

 crowded with delicately tinted pink florets. Both the main stem and 

 the branches are horny and closely annulated. In the details of the 

 anatomy of the polypites there is practical identity with those of 

 Syncoryne. In Goryne, however, the polypite is considerably larger, 

 but it is solely the divergence of the reproductive plan that entitles 

 this species and its congeners to the dignity of a separate genus. 



The colonies are again unisexual, some bearing only male 

 buds, while others bear female ones. These appear as numerous 

 rounded bodies clustered on the polypites between the bases of 

 the tentacles. The male ones consist solely of masses of cells — 

 spermatoblasts — which produce spermatozoa ; while each of the female 

 buds becomes filled with 20 to 25 large ova. When the male 

 capsules burst, it is probable that the spermatozoa find their way 

 to the female organs, guided by some sense or attraction we know 

 not what, and pierce the membranous envelope, thereby gaining 

 admission to the ova. The latter, thus fertilized, by segmention form 

 tiny embryos, which issue forth as four-armed hydriform larva?, that 



