THE ANTHOZOA 



47 



exocoeles. But Hertwig's description is inconsistent with his 

 figures, in which twenty couples of mesenteries are shown, of which 

 eight couples are complete, and the position of Polyopis must be 

 considered doubtful for the present. 



Sicyonis crassa has sixty-four mesenterial couples sixteen com- 



b. 



Fio. XXII. 



1. Diagrammatic transverse section through the stomodseal region of Tealia crassicornis, 

 1, 1, primary mesenteries ; 1", 1, precociously developed mesenteries of the second cycle ; 2, 2, 

 normal mesenteries of the second cycle ; 2", 2, precociously developed mesenteries of the third 

 cycle. 



2. A similar section of Polyopis striata. 1, 1, mesenterial couples of the first cycle ; 2, 2, 

 mesenterial couples of the second cycle ; 3, 3, mesenterial couples of the third cycle ; x, x, the 

 dotted lines represent mesenterial couples figured by Hertwig, but stated in his description to be 

 absent. If they were present they would complete the second cycle. All the mesenteries are said 

 by Hertwig to reach the stomodaeum, but his figure represents the primaries only as complete. 

 Hence the inner ends of the secondaries and tertiaries have been represented in dotted lines. 



3. A similar section through Sicyonis crassa. Numerals as in 1. There are really sixty-four 

 mesenteries in Sicyonis, but to avoid crowding the figure the number has been halved. 



4. A similar section through Scytophorus striattts. Numerals as in Fig. XXI.; x,x, additional 

 pair of asulco-lateral mesenteries. 



5.Gonactinia proli/era. Numerals as in'Fig. XXI. ; y, y, two additional mesenterial couples 

 in the sulculo-lateral chambers. 



6. Oractis diomeckae. Numerals, etc., as in 5 ; z, z, additional mesenterial couples in the 

 transverse chambers. 



plete, sixteen incomplete forming the second cycle, and thirty-two 

 incomplete forming the third cycle. Only the mesenteries of the 

 third cycle bear gonads (Fig. XXII. 3). Here, Boveri suggests, 

 the mesenterial couples numbered 1 are the true primaries, to which 

 the two couples numbered l a , belonging really to the second cycle, 

 are added, making an apparent primary cycle of eight couples. The 

 apparent second cycle of eight couples is made up of the four 



