134 MR. W. L. SCLATER ON A NEW [Feb. 16, 



The ectoderm of the tentacle (Plate XIII. fig. 6) also contains a 

 series of neniatocyst batteries ; the cells, however, differ from these 

 of the knob in the following points: they are very much smaller, 

 they are pigmented, from them are developed the longitudinal muscle- 

 fibres ; in the endoderm of the main part of the tentacle the elements 

 are not nearly so high as are those of the knob, and at their bases 

 are found the circular muscle-fibres. 



The tentacle therefore differs little in structure from the actinian 

 type as described by Hertwig (7). 



The muscles are very well developed on both sides of the mesen- 

 teries ; the arrangement is shown in figures 8 and 9 of Plate XIV., 

 where figure 8 represents the arrangement on the ectocoelic face, 

 figure <J the arrangement on the entocoelic face. The edge of the 

 mesentery is occupied by a thick packed mass of mesenteric filaments 

 above, and by the ova, also packed thick, below ; ova and mesenteric 

 filaments seem to be well developed in all the mesenteries, except on 

 the directives, where I have been unable to detect any sign of ova, 

 but I have only been able to examine two directives, one of which 

 was malformed, so that I am unable to make sure of this point, 



Plate XIII. fig. 7 represents a small portion of a section of a 

 mesentery highly magnified, showing the folding of the surface on 

 one side in order to increase the surface for tlie mustle-slips, but in 

 no case have I detected the inclusion of masses of muscles in the 

 mesoderm, as has been figured by Hertwig (7) in Actinoloiia and 

 Tealia, and other Actiniae. 



The only example of this Coral I have been able to examine con- 

 tained ova ; no spermatozoa could be detected, so that the Coral may 

 be considered dioecious. 



The develnpnient of the ova differs slightly from tiiat described in 

 the Actinians by Hertwig ; in Stephunotrochus the mesodermtd lamella 

 in which the ova lie is reduced to a thin string (Plate XIV. fig. lO), 

 and the entodermal cells on either side have become very long and thin, 

 resembling, perhaps, the "Cambium Zellen " described by Weissman 

 in certain Hydroids which nourish the ova at their own expense. In 

 the figure tliere will be seen several ovarian cells which have not yet 

 entered the mesodermal lamella, but which are still Iving in the 

 endoderm ; and in one case there is an ovarian cell figured lying iialf 

 in the endoderm and half in the mesodermiil lamella ; the ripe ovum 

 is full of deuto})lasm, and the germinal vesicle and germinal spot are 

 very clearly seen. 



Besides the ovarian siring, the mesenteric filaments can be seen in 

 section ( Plate XIV. fig. iOj, consisting of a mesodermal string and 

 higii endodernial cells, with many pigment-cells scattered among 

 them ; they are cut in section in different planes. 



Beyond the ova the mesoderm again thickens slightly up to the 

 end of the mesentery, where it splits to line the hard septal walls, 

 since this section is from part of the mesentery low down where the 

 mesentery is inserted between the columella and the two adjacent 

 septa, all of which are lined by the mesodermal lamella with a layer 

 of calycoblastic cells interposed. 



Calycoblastic cells were first detected by Hcider (8), who showed 



