120 Proceedings of the Royal Irish Academy. 



animal as a whole presents a superficial resemblance to Hertwig's Polysi- 

 phonia tuberosa. but the tentacular plan, as well as other details, is quite 

 different. 



- ucture. — (i) Mesenteries. I carefully dissected three specimens. There 

 are five cycles of mesenteries, and faint traces of the beginning of a sixth in 

 the largest specimen. The first two cycles are quite perfect, the third-cycle 

 mesenteries run less far down the actinopharynx, and the fourth cycle is 

 only just perfect. Total) 96 pairs; arrangement, hexamerous. First two 

 cycles sterile, third with a few gonads, fourth and fifth very fertile. Small 

 oral stomata are present, but ii" marginal ones. In two specimens, the 

 fourth-cycle mesentery-pairs all had one individual quite clearly larger than 

 the ether, and in those of the fifth cycle the difference in size in each 

 pair was extremely marked. The inequality in all cases, and with no exeep- 

 tions, followed the rule laid down tor this genus by Carlgren in 1893, and 

 which is given above in the definition of the sub-family. In the third 



mien, the smaller partner of each fifth-cycle pair was too small to be 



a with the naked eye; but by microscopic examination I satisfied 

 myself that, at any rale in the piece of the animal examined, the smaller 

 partner was really there in the right position, hut had not yet grown out 



■nd the endoderm, so no doubt the rule prevailed here as in the other 

 two specimens. The inequality of the mesenteries is not confined to the 

 fourth and tilth cycles, hut i- less marked in the oth 



Sections I ir of the animal reveal the following details: — 



—The -mailer partner in each pair lias or has not a filament, 

 hut it has a -mall parietal muscle, although no gonad or definite retractor. 

 The larger partner has a large gonad and filament, with a fringe of stout 

 longitudinal mm esses on the endocoelic face, and a streak of trans- 



On the other. 



The fourth-cycle _•■ gonads, but the muscular portion 



of one partner much hat of the other. They have a parietal muscle, 



tending to be differentiated into parietobasilar and longitudinal hah."-, and 

 a distinct diffuse pennon, which ceases abruptly at it- distal edge. As the 

 body-wall i- hed it- process.'- b gradually lower and - 



instead of Blender, branched, and tree-like. The mesogloea of the mesen- 

 teries, here and in the ol eloped. 



The third-cycle mesenteries have the whole of the endocoelic face of their 

 muscular part i » diffuse pennon, who-.- proc a Btarl imme- 



diately at the body-wall, and rapidly become high. It tapers at Loth ends, 

 the highest part being nearei the distal side than the proximal. In its best- 

 developed part the mesogloea of the mesentery is produced into rather 



