310 ME. J. E. DFBRDElSr ON 



being provided with mesenterial filaments. They therefore 

 correspond with the oldest stage in Lehrunia. The endoderm, 

 however, had already arranged itself into a somewhat definite 

 layer, but lying scattered about in the body-cavity of the embryo 

 were numerous, somewhat large, cellular elements and yolk- 

 granules. 



The Zoanthid larva which van Beneden (1890) identified as 

 closely related to Semper's Jarva presents three pairs of complete 

 mesenteries and four incomplete pairs, and a very thick endo- 

 derm, with small coelenteric spaces within the stomodaeal region. 

 Below, however, a considerable gastro-vascular cavity is formed. 

 The same author (1891) found the larvae of the Cerianthid 

 Arachnactis^ at the stage with only one pair of mesenteries and 

 two pairs of tentacles, to possess a ccBlenteron fully formed with 

 an endodermal lining of only a single layer of cells. Prof. Gr. von 

 Koch observed a central cavity in Gorgonia and in CaryopJiyllia 

 cyathus (1897) before the formation of any mesenteries or the 

 production of an oral aperture and stomodaeum. 



In the newly-hatched larva of EupJiyllia rugosa, Haddon (1890) 

 found three of the twelve pairs of mesenteries already bearing 

 filaments, and alternating with the mesenteries were " large 

 ridge-like vesicular outgrowths from the endoderm.''' There can 

 be little doubt that, as in Lehrunia^ these latter are the detached 

 survivors of a more or less solid vacuolated tissue in the earlitr 

 stages of the larvae. Prof. E. L. Mark (" Selections from 

 Embryological Monographs," pi. xii. fig. 32) figures similar inter- 

 mesenterial protrusions, thoroughly vacuolated, in JEdwardsia. 

 The appearances should be compared with fig. 19 and with the left 

 side of fig. 20 (PI. 19) in the present paper. The phenomena are 

 remarkably alike. On plate xiii. fig. 15 of the same publication, 

 Prof. Mark reproduces the transverse section of the larva of 

 Balaiiophyllia regia given by E. Jourdan, in which the embryo 

 is still solid, though the central portion is indicated as yolk. 

 Six mesenteries are here shown and the internal yolk seems 

 clearly separated from the endoderm, which latter is still many 

 cells in thickness. The conditions appear to be somewhat com- 

 parable with those in fig. 14 (PI. 18) of Lehrunia. I regret ex- 

 ceedingly that, not having Jourdan's original memoir for reference, 

 I can do no more than merely draw attention to the possibility of 

 larval coelomic spaces being present in such a case. The thick 



