THE EDWARD SI A-STA&E Of LEBRUNIA. 275 



arising from the most distal region of the column and bearing 

 spheroidal batteries of nematocysts. The mouth, instead of 

 being circular, is very long and narrow. 



Prom what we already know of the development of other 

 Zoantharia, the hesameral character of the adult tentacles is in 

 most cases derived from the readjustment of primary tentacles 

 of different sizes and origin. Thus, already in the larvae the first 

 cycle of six is indicated, constituted of the four larger of the 

 eight primary tentacles and two of the smaller. The remaining 

 two will probably form one of the pairs of the second cycle of 

 six tentacles alternating with the first, in which case it is obvious 

 that the second cycle will be composed of individuals of a very 

 difi'erent order of development. 



As regards the tentacles, then, Lehrunia coralUgens passes 

 through three very distinct stages : — (1) a tetrameral radial 

 symmetry, with four large and four small tentacles ; (2) a bi- 

 lateral symmetry of the same parts, six tentacles being nearly 

 equal and forming one cycle, and two remaining smaller and 

 outside the others ; (3) the approximate hexameral radial 

 symmetry of the adult, with numerous alternating entacmseous 

 cycles. 



The simultaneous appearance and tetrameral radial arrange- 

 ment of the tentacles here described in the first stage is in 

 marked contrast with what is known of the tentacular develop- 

 ment of the Zoantharia generally. 



Comparatively few observations on the order of appearance of 

 the tentacles have, however, been recorded. One of the fullest 

 and best is the well-known account given by Prof, de Lacaze- 

 Duthiers of the growth of Actinia equina, and supplemented by 

 observations on other species. Not having the original mono- 

 graph for reference, for what follows I am. dependent upon the 

 many figures and details reproduced by Prof. E. L. Mark in his 

 " Selections from Embryological Monographs " (1884), and by 

 Prof. A. C. Haddon in the concluding portion of his " Revision 

 of the British Actiniae " (1889). Prom these it appears that the 

 dorsal tentacle is the first to arise, and for a long time this 

 predominates over the others. The octoradiate stage quickly 

 supervenes, the median lateral tentacles being the next largest 

 to the dorsal, and the ventral protuberance one of the smallest. 

 The great difference in size between the dorsal and ventrai 



