BAMFORD— PELAGIC ACTINIARIAN LARV^ 397 



globules, like yolk globules. The muscular fibres form a single layer and parieto-basilar 

 muscles are present. 



Loc. Off Salomon Atoll, Chagos Archipelago, surface ; two specimens. 



One specimen has been cut into transverse and the other into longitudinal sections. 

 The former has the mesenteries in the stomodseal region arranged on one side in the 

 microtype manner and on the other in the macrotype. 



The arrangement in the other larvae of the genus is that the dorsal-directives are 

 incomplete mesenteries, viz. do not meet the stomodaeum and have no filaments, while the 

 ventral directives, being complete, fuse with the stomodeeum and have filaments; laterally, 

 complete and incomplete mesenteries alternate from the dorsal to the ventral side, the 

 whole arrangement being the microtype. In the larva now referred to, on the side with 

 the macrotype arrangement, the mesentery next but one to the dorsal directive is complete 

 in that it extends to the stomodseum throughout its length, but it is not provided with 

 a filament on its free edge. In the cases referred to as described by Duerden it is the 

 usually incomjjlete mesentery of the second pair from the dorsal directives. 



3. Larva III. Zoanthina sladeni, n. sp. (PL 23, figs. 5, 6.) 



The specimen is 1*5 mm. long by 1"125 mm. in diameter ; its colour is white. The 

 pedicle is comparatively long and the circular groove deep. The oral part is marked by 

 twelve longitudinal depressions, but the aboral part is not grooved ; no tentacles are 

 present. 



The stomodseum extends to the circular groove and is a fissure-like opening at the 

 base of a rather ovoidal buccal orifice ; no ridges are present. The mesenteries reach from 

 the oral to the aboral pole, and towards the latter both extend almost equally into the 

 coelenteron ; in the pedicle the incomplete mesenteries are minute. There is no aboral 

 pore, but the centre of the aboral surface is depi'essed externally and this gives rise 

 to an upgrowth within the coelenteron, in some sections simulating the pillar found in larvae 

 I. and II. 



A peculiar feature of the mesenteries is the development of endodermal outgrowths as 



in fig. 6. They are circular in section and consist of much vacuolated endoderm with 



a central axis formed by the structureless lamella ; neither gland cells nor nematocysts 



occur in them. On examining sections from the oral to the aboral end, these outgrowths 



are seen near the base of the stomodaaum, and there they are fused together. Near the 



base of the circular gi'oove 6 are distinct, 5 in a circle with 1 in the centre. Towards the 



aboral end the complete mesenteries are bent sharply back from the centre of the 



coelenteron on the side opposite the muscles. At these bends the structureless lamella 



and the endoderm of the outgrowths are fused up with the corresponding structures of 



the mesenteries, more aborally appearing to be the direct radial continuations of the 



mesenteries on which the filaments look like appendages (fig. 6). Nearer the base the 



filaments stop, and the mesenteries left are in half their breadth formed of the above 



outgrowths*. Similar endodermal swellings are found on the free edges of the incomplete 



mesenteries. 



* It is useless to speculate on the function or the homologies of the outgrowths here described, as there is 

 only one larva and the early stages of its development are quite unknown. 



