298 ME. J. E. DFEEDEN ON 



one of apparently continuous growth in pairs of tlie tentacles 

 and mesenteries. 



Prom the few examples given there is evidently little or no 

 connection to be expected between the stage o£ internal develop- 

 ment and the appearance of the tentacles. 



In viviparous polyps the formatiou of the tentacles rarely 

 takes place until the larvse are set free, whereas the internal 

 development may have proceeded to almost any degree, though 

 apparently not often beyond the Sdwardsia-^tage. Yet in newly- 

 hatched larvse of Aulactinia I found examples with six tentacles 

 already protruding. 



The relation of the axis of symmetry of the tentacles in their 

 bilateral stage with that of the mesenteries may now be con- 

 sidered. 



In Actinia eg'M^V^ffl Lacaze-Duthiers found the first and largest 

 tentacle to arise from the sulcular endocoele, a smaller and 

 opposite from the sulcar endocoele, and the three lateral pairs, 

 varying somewhat in size, from the lateral mesenterial chambers. 

 The sagittal axis of the tentacles, therefore, is the same as the axis 

 of symmetry of the paired mesenteries, a relationship which would 

 naturally be expected. The longer axis of the stomodseum is also 

 in the same plane. The figures of McMurrich and van Beneden 

 show that in Arachnactis the plane of symmetry of the tentacles 

 and of the mesenteric chambers likewise coincide, and von Koch 

 represents the same relations for Garyopliyllia cyathus. 



In one late larva of Lehrunia, in which a complete series of 

 transverse sections enabled these relationships to be followed from 

 one end to the other, a different relationship was encountered. 

 This is represented in PI. 19. figs. 23-25. 



The first section (fig. 23), passing through the basal tentacular 

 region, exhibits the relative sizes of the tentacles such as has 

 already been described among the external characters for the 

 bilateral stage. Sections in advance of this leave no doubt as to 

 the correctness of the dorso-ventral relations here indicated. 

 The longer axis of the oval stomodseum is in a plane at right 

 angles to that of the median axis of the tentacles. Fig. 24, 

 taken from a section through the middle stomodaeal region, re- 

 veals the same bilateral arrangement of the tentacles, but the 

 dorso-lateral tentacles (_/, Ji) are now comparatively larger than 

 before on account of their relatively lower origin in the polyp. 



