No. 3.] MORPHOLOGY OF THE ACTINOZOA. 323 



mesenterial spaces between the third and fourth pairs of mesen- 

 teries. Upon the mesenteries the longitudinal muscle processes 

 have begun to appear. The manner of their arrangement may- 

 be better seen, however, from an older specimen, a figure of which 

 is given (PI. XIII, Fig. 19). It will here be seen that the em- 

 bryo is bilaterally symmetrical, the line separating the antimeres 

 passing between the mesenteries of the third and fourth pairs, 

 and therefore in the direction of the elongation of the stomato- 

 daeum. The mesenteries of the third and fourth pairs are seen 

 to have their longitudinal muscles on the faces which are turned 

 away from each other, and accordingly correspond to the direc- 

 tives of the adult. The mesenteries of the first and second 

 pairs do not form a pair in the same manner as the directives, 

 but each mesentery of these pairs has its longitudinal muscles 

 upon the face which is directed towards the third pair of mesen- 

 teries, which we may term the ventral directives. 



We have then in this stage an arrangement which exactly 

 reproduces the condition permanent in the Edzvardsice, and 

 which may therefore be termed the Edwardsia stage. The sig- 

 nificance of this from a phylogenetic standpoint I have already 

 elsewhere pointed out ('89), and do not intend to enter into this 

 question here, hoping to return to it with a discussion of other 

 investigations on the subject in a future number of these 

 " Contributions." 



The next stage witnesses the formation of two additional 

 pairs of mesenteries, which make their appearance simulta- 

 neously upon either side of the mesenteries of the first pair 

 (Fig. 19). These grow rapidly, finally reaching the stomato- 

 daeum, and developing their longitudinal muscles. Twelve per- 

 fect mesenteries are then present. The mesenteries of the fifth 

 pair have their longitudinal muscles on the face which is turned 

 towards the mesenteries of the first pair, and those of the sixth 

 pair have them on the face which is turned towards the mesen- 

 teries of the second pair, i.e. upon the dorsal surface in each 

 case. When these youngest mesenteries have become perfect 

 we have a stage which exactly resembles the condition perma- 

 nent in Halcainpa, and which, therefore, may be termed the 

 Halcampa stage. 



The mesenteries are arranged in six pairs. Two of these, 

 occupying the dorsal and ventral surfaces, are formed each of 



