Royal Physical Society. 449 



The characters of Atractylis are : — 



Atractylis. — Polypary sheathed, creeping, erect, or branched. Polyps 

 fusiform, incompletely retractile, with transparent filiform, alternating 

 tentacles (mouth closed by a dense muscular ring). Thread-cells incon- 

 spicuous. Reproduction by medusoids. 



Atractylis ramosa (VanBeneden, Dalyell). — Polypary sheathed, erect, 

 and branching ; stem composed of many minute sub-parallel tubes ; ends 

 of branches dilated. Medusoids springing from branches and polyps; 

 umbrella sub-giobose ; peduncle with four undivided capitate tentacles ; 

 marginal tentacles eight, in four pairs, each pair springing from a bulb 

 having two eye-specks ; auditory sacs absent.* 



ovicapsules). Those I have met with form a cluster round the base of the ten- 

 tacles, and are arranged in a linear or moniliform series, two or three on each 

 pedicle." The double sperm sac consists of two ectodermic sacs placed end to end 

 (Plate II., fig. 1, a, 5), permeated by a tubular process of endoderm (c), and 

 containing the spermatic gelatinous plasma. As the spermatozoa first ripen in 

 the distal sac (d), the endoderm in that sac is absorbed and withdrawn. The 

 same process afterwards takes place in the proximal sac (e). The ovarian sac 

 (fig. 2, a), contains a single yellow ovum (6), which at an early stage is encircled 

 by a looped tubular process of the endoderm (c) ; subsequently this loop is ab- 

 sorbed, and the ovum becomes a ciliated larva filling the sac. Its further 

 change has been described by Dalyell. 



* Note on the development of Bourgainvillea Britannica from Atractylis ra- 

 mosa. — In August last I found Atractylis ramosa growing in great profusion on 

 the Bimer Rock and on Inchgarvie, both near Queensferry, Firth of Forth. 

 When taken, the specimens were in high condition, each branchlet possessing 

 its terminal polyp ; but after being kept in one of my tanks for a few days, I 

 found that a great change had taken place; the polyps were all absorbed, or 

 undergoing the process of absorption, and in their place, and also from the 

 branches themselves, a great number of medusa buds were put forth, which 

 were rapidly developed into the Medusa ocilia of Dalyell. The zoophyte had 

 in fact assumed its reproductive phase. It had changed from a creeping hydra- 

 bearing zoophyte, to a multitude of free and actively swimming medusae. It 

 is well known that the Aphis, as long as its pasture is good and the weather is 

 fine, will produce a continued succession of wingless and sexless individuals by 

 internal gemmation. It will continue its phase of nutrition. But should its 

 circumstances fall adverse — should Flora and Jove become unpropitious — then 

 it undergoes its last change, and becomes a winged and egg-bearing creature. 

 It assumes its phase of reproduction. So the gluttonous caterpillar, taken yet 

 unsatisfied from his cabbage leaf and shut up in a box, becomes prematurely a 

 chrysalis. And so, too, the medusa-bearing zoophytes, exchanging the open sea 

 for the confined water and poor fare of a tank, become, so to speak, winged 

 medusae, and, instead of a continued succession of polyps, produce eggs. 



The medusa of Atractylis ramosa, when first given off" from the zoophyte, is 

 identical with the Medusa ocilia of Dalyell. The orange-coloured alimentary 



