450 Proceedings of the 



Atractylis repens (mihi). — Polypary creeping, sheathed; polyp-stalks 

 erect, single, or bifurcate (wrinkled) ; ends of stalks dilated or not. Medu- 

 soids springing from polyp stalks, mitre-shaped ; peduncle quadrangular ; 

 tentacles four, two very long, two rudimentary. Eye-spots and auditory 

 sacs absent. 



Atractylis sessilis (mihi). — Polyps sessile on creeping polypary, or 

 scarcely stalked, sheathed up to the tentacles. Medusoids developed from 

 creeping fibre, similar in shape to those of Atractylis repens. 



On the fixed Medusoids of Laomedea dichotoma. 



Description of Plate. 



Plate XXIII. 

 Fig. 3. Summit of reproductive capsule (female) of L. dichotoma — a, four- 

 lobed endodermal or nutritive process of ovarian sac — 6, ectoderm 

 of do. — cZ, umbrella or marsupium — e, ectoderm of ovary ruptured, 

 ova having escaped into the cavity of the marsupium. 



4. Summit of male reproductive capsule of L. dichotoma. 



5. Alimentary polyp of Siphonophorous Zoophyte (Agalmopsis punctata), 



and 



6. Tentacular polyp of same, compared with 

 7 and 8. The same organs in Sarsia. 



polyp or peduncle has four unbranched tentacles, capitate at their extremities 

 with bundles of thread-cells. The orange tentacular polyps are each furnished 

 with two tentacles, and a black eye-speck at the root of each tentacle. In this 

 stage a large number, then about a month old, were brought to Edinburgh. 

 They fed on the minute Entomostracea (which swarmed in the tank), with 

 avidity, and increased in size. But, to my surprise, I found that a further de- 

 velopment was taking place in them. The tentacles of the alimentary polyp 

 (peduncle) became first once, and afterwards twice, dichotomously divided, and 

 each of the tentacular polyps put forth additional successive tentacles, until the 

 greatest number observed amounted to six, each additional tentacle being accom- 

 panied by an additional eye-speck at its root. At the same time, genital lobes 

 were developed, springing from the peduncle, which passed for a short distance 

 along the lateral canals of the sub-umbrella, and ultimately contained sper* 

 matozoa. In other specimens, given off by Atractylis ramosa in the spring, but 

 which never arrived at so late a stage of development, ova were found situated 

 in four masses within the walls of the peduncle. This medusa, at its latest 

 stage of development observed by me, bears a strong resemblance to the Hip- 

 pocrene or Bourgainvillea cruciata of Forbes, and also to his Bourgainvillea 

 Britannica, which I am disposed to consider as different sexes and stages of 

 development of the same medusa. I am the more emboldened to hold this 

 opinion, as Professor E. Forbes has already considered the Medusa duodecilia 

 of Dalyell (which represents, as I have observed, one of the stages of that I am 

 now describing) the same with his Bourgainvillea Britannica. [Monograph of 

 British Naked-eyed Medusce, p. 68.) — Nov. 22, 1858. 



