1 64 McMURRICH. 



EXPLANATION OF PLATE. 



The numbers I-IX denote the primary and secondary mesenteries in the order of 

 their appearance. 



Fig. i. Diagrammatic figure of a section of Metridium marginatum, with only 

 one siphonoglyphe. 



Fig. 2. Transverse section of the column of Halcampa producta below the level 

 of the stomatodseum. 



Fig. 3. Transverse section of a primary mesentery of Halcampa producta to show 

 the muscle pennon. 



Fig. 4. Transverse section of the column of Oractis diomedece. 



Fig. 5. Longitudinal section of Zoanthid larva with twelve mesenteries. <r;- = ring 

 of cilia. 



Fig. 6. Transverse section of column of Zoanthid larva with twelve mesenteries. 



Fig. 7. Transverse section of Zoanthid larva with twenty mesenteries. 1 r, 2 r = 

 first and second pairs of ventro-lateral mesenteries of right side; I /, 2/= first and 

 second pairs of ventro-lateral mesenteries of left side. 



Fig. 8. Transverse section of imperfect mesentery of Zoanthid larva with twelve 

 mesenteries. <r — ectoderm ; 11 = nerve tissue; gr = granular tissue below the nerve 

 ring; mg= mesogloea; ^»=endoderm; mc = mesenterial canal. 



Fig. 9. Transverse section of larva of Arachnactis brachiolata with four tentacles. 

 t 1 = first formed tentacles; t 2 = second tentacles. 



Fig. 10. Transverse section of larva of Arachnactis brachiolata with six tentacles. 

 t 1 , t 2 , t 3 — first, second, and third tentacles. 



FlG. II. View of the dorsal side of larva of Arachnactis brachiolata with seven 

 tentacles. /= lip. 



FlG. 12. View of ventral side of larva of Arachnactis brachiolata with seven ten- 

 tacles. Lettering as in preceding figure, except I* = unpaired ventral tentacle. 



FlG. 13. Transverse section of larva of Arachnactis brachiolata with seven ten- 

 tacles. 5 = first pair of Cerianthan mesenteries. 



