.2 ZOANTHARIA 



Anatomical description. The ectoderm of the body-wall is large, continuous and richly 

 incnisted. It contains sparse, uniformly broad nematocysts with greatly twisted thread (length 31— 36/^, 

 breadth 12^). The mesogloea is fairly thick, mostly incrusted and contains a few large cell-islets and 

 now and then cell-groups, surrounded by inconsiderable protoplasm (PI. 6, fig. i). The entoderm is thin. 

 In the capitular region the ecto- and entoderm become thicker, especially the former, while the meso- 

 glcea gets thinner. 



The sphincter is straight with few folds, the musculature strong. 



The longitudinal musculature of the tentacles is strong. Tlie spirocysts of the ectoderm very 

 ntimerous, whereas the thick-walled nematocysts are scarce, about 22 fx long sometimes smaller. 



The oesophagus is almost without longitudinal folds, probably because it is very much expanded. 

 The ectoderm contains numerous thick-walled capsules (length 17— 24/^x6 «) and is several times 

 thicker than the mesogloea. In the distinct siphonoglyphe the mesogloea is considerably thickened, 

 especially where the directive mesenteries are attached. The ectoderm of the siphonoglyphe is thinner 

 than in the oesophagus. 



The number of mesenteries is 28—32, i. e. less than in /. ardoresccns though the latter has a 

 much smaller diameter than /. hitlbosiis. 9 specimens examined had 28 mesenteries, i had 32 and 3 

 had 30, 9 macro and 7 micro on the one side and 8 macro and 6 micro on the other. In one case at 

 least the right side was the most developed. The mesenteries are thin, somewhat thickened inwards 

 and extending below the oesophagus a long way into the gastrovascular cavity, the micro-mesenteries 

 are thin but become broader below the oesophagus. The lamella of the longitudinal muscle is fairly 

 well-developed especially just below the cesophagirs, where it is provided with some closely-lying folds. 

 The parieto-basilar muscles are weak. The longitudinal and parieto-basilar muscles extend some 

 distance out onto the body-wall. 



The structure of the filaments is typical. The glandular tract contains sparse thick-walled 

 nematocysts broader at the one end and with distinct basal part to the spiral thread (length 19 — 22 (24)//, 

 breadth 6/^), further there are also granular thick-walled capsules (length 26— 31//, breadth 5/^, .some- 

 times smaller). In a specimen from St. 32 I found some very few small egg-shaped capsules (length 

 10— ii;u, breadth 4 /<). These may possibly also be present in other .specimens but owing to their 

 small size and scarce occurrence may easily have escaped notice. The large nematocysts with greatly 

 twisted thread are very seldom observed (length about 36 y«, breadth 12 /i) and are generally absent 

 altogether. I have examined these nematocysts of the filaments in various specimens from different 

 localities and found them in the main to be in agreement with each other. It seems characteristic, 

 that the nematocysts with greatly twisted thread are extremely scarce if present at all. Nor do smaller 

 nematocysts of the same kind as the preceding seem to occur, in contrast to what we find in man)- 

 other Isozoanthus-species, or if occurring are extremely scarce. In their place thick-walled nematocysts 

 of a somewhat granular appearance may be observed. 



The polyps are di(x;ciou.s. 



