ACTINIARIA 



109 



character, the muscle-layers almost all waning, and the mesogloea and the endoderm attenuated. The ecto- 

 derm of the acrospheres is very high, in comparison with the thin mesogloea and the endoderm. It contains 

 large nematocysts, most densely packed, arranged like palisades, of equal width and of variable size, from 

 48 to 106 X 2 ;JL, occupying almost the whole height of the ectoderm. Besides these, there are a little broader 

 nematocysts with visible basal part to the spiral thread, 7298 X 3,54 fi in size. The ectodermal and the 

 endodermal muscles are absent or represented by very few muscle-fibrillae. The stalk of the tentacles is of 

 another structure (fig. 137 lower part). The ectoderm is thinner than in the acrospheres and of about the 



Fig. 136 



Textfigs. 136 139. 

 Haloclava producta. 



Fig. 136: Longitudinal section through part of the column 



with papilla. Fig. 137: Longitudinal section of the distal 



part of tentacles with acrosphere. Fig. 138: Transverse 



section through part of a tentacle. Fig. 139: Transverse 



section of a mesentery in the reproductive region. 



Im: longitudinal muscles; cm: circular muscles. 



Fig. 138 



same thickness as the mesogloea, the folds of the mesogloea included. It contains gland-cells and numerous, 

 but small nematocysts, 13 17 X 2 ;i in size. The ectodermal longitudinal muscle-layer is very strong with 

 densely packed, high folds (textfig. 137 Im; textfig. 138, transverse-section through a piece of the basis of 

 a tentacle) , which are sometimes not ramificated, sometimes near the basis bifid or trifid. The main lamella 

 of the mesogloea is thin, fibrillary with rather few cells. The endoderm is of about the same thickness as the 

 ectoderm, the endodermal circular muscles somewhat strong, through the folds are rather large. 



The ectoderm of the oral disc and of the tentacles is devoid of spirocysts, the nematocysts are 

 somewhat sparse and of the same size as in the stalk of the tentacles. In maceration-preparations I also found 

 nematocysts resembling those of the actinopharynx. As the specimens were very much contracted in the 

 region of the oral disc, it is, however, possible that these nematocysts in reality belong to the actinopharynx. 

 The radial muscles were considerably weaker than the longitudinal muscles of the tentacles. The ectoderm 

 of the actinopharynx is much higher than the endoderm, and several times thicker than the mesogloea. It 



