332 J. E. Duerden — Jamaican Actiniaria : Part I. — Zoanthece. 



ZOANTHE-ffi (continued). 



Macrocnemisle. 



Bpizoanthus minutus, n. sp. 



Parazoanthus Swiftii (Duchassaing and Michelotti). 



All the examples having been partially studied in their living condition, and 

 generally from an abundant supply of material, it has not been possible in some 

 cases to draw up the specific characters in very hard and fast terms. The few 

 external features one has to depend upon in the Zoanthidse are well known to all 

 workers in the group to be very variable ; and especially will this be seen to be 

 the case in the genera Zoanthus and Palythoa. 



Recognizing the form of the sphincter muscle as of great importance in specific 

 identification, I have figured it in all cases. 



Practically all the material has been preserved by simple immersion in a 

 four or five per cent, solution of formalin. Owing to the presence of abundant 

 incrustations and the great thickness of the mesoglcea, the internal tissues of the 

 Zoanthidas are rarely well preserved. It is satisfactory to find that, by means of 

 formalin, the preservation and histology was, in every case, all that could be 

 desired, while, in most, little alteration of form or dimensions occurred ; thus 

 allowing the number of capitular ridges and tentacles, measurements, etc., to be 

 taken at leisure. The colours can likewise be observed for some time, but 

 disappear ultimately. 



A curious chromatic change occurred in most of the Palythoa material. The 

 colonies, usually cream colour when alive, became strongly brick-red in their 

 upper region after immersion for a short time in the formalin. This alteration 

 extended also to the ectoderm of the oesophagus and to the mesenterial 

 filaments. 



Some importance must be attached to the method of preservation in determining 

 the appearance of the various histological characters. With alcohol the mesoglcea 

 shrinks very considerably. To this disproportionate shrinkage, compared with 

 that of the ectoderm and cuticle, is due the contorted or dendriform appearance 

 of the outer part of the body-wall often seen in species of Zoanthus. The size 

 and appearance of the mesoglceal cavities, especially those containing the sphincter 

 muscle, may be much modified. Figs. 1, 2, and 3, on PI. xviii.a, should be com- 

 pared. The last having narrow, almost closed cavities, was drawn from a polyp 

 shrunk in alcohol, and the two first from colonies preserved without shrinkage 

 in formalin. Specimens of Z. pulchellus preserved later in formalin show open 

 cavities like figs. 1 and 2. The figure of the cavities of the sphincter muscle 

 of Zoanthus, sp. ?, given by Hertwig (1882, pi. xiv., fig. 1), is evidently partly 

 determined by this shrinkage. 



