TYPE CCELENTERA. 



Ill 



4. Order Antipatharise. 



The members of this order are all colonial and secrete a 

 branching axial skeleton of a black horny material. The 

 polyps possess usually but six simple tentacles, and as a rule 

 only six mesenteries are present, of which only the two lying 

 in the transverse axis bear reproductive organs and mesen- 

 terial filaments ; in some forms four or six additional imper- 

 fectly-developed mesenteries are present, but six seems to be 

 the number typical for the group. 



5. Order Protactinise. 



This order includes a group of forms, all simple and with 

 simple tentacles, but showing considerable variation in the 

 number of the tentacles. They all 

 agree in this particular, however, 

 that there are twelve mesenteries 

 arranged in pairs (Fig. 63, I-V1\ 

 the two pairs attached to the si- 

 phonoglyphe region of the stoma- 

 todieum having their retractor 

 muscles on the faces turned away 

 from each other, while in the other 

 four pairs they are on adjacent 

 faces. The two former pairs are , 



termed the directive mesenteries FlG . GS.-DIAGRAMMATIC TRANS- 

 (Fig. 63, D and D'}, their constit- VERSE SECTION OP Gonactinia. 

 uent mesenteries lying one on each ' D> = directive mesenteries, 

 side of the sagittal plane, and to- Z ~ IV '- the Edwardsi an niesen- 



gether with one mesentery (//and v> VI = ries forming 



/) from each of the other pairs pairs with //and I. 



represent the eight Edwardsian 7 ~ secondary pair of mes- 

 inesenteries. To these six primary 



pairs a varying number is added in the different forms ; it 

 may be, on each side, one between one of the pairs of direc- 

 tives and the adjacent lateral pair (Scytopliorus), or a pair in 

 the same locality (Gonactinia, Fig. 63, 7), or two pairs one of 

 which corresponds to the pair of Gonactinia, the second pair 

 lying between the two lateral primary pairs (Oractis). 



