32 Coelenterata. 



6 to 10 feet after the period of greatest depression. They do not form a true 

 atoll. A list of the Anthozoa and Hydrocorallia found in the reefs is given, 

 and descriptions and figures of many of them are added, including Mussa 

 1 n. sp., 1 n. var., Aiptasia 1 n. var., Actinia 1 n. var., Bwiodactis 2 n. var., 

 Epicystis 1 n. subsp., Plexaura 1 n. nom., Plexauropsis n. 1 n., Euniceopsis n. 

 (for those species of Eunicea in which column and tentacles contain double 

 rows of spicules which are absent in typical specimens of Eunicea s. str.). - 

 See also Bericht f. 1903 Coel. p 5, 21 Verrill. 



B. Alcyonaria. 



See Harrison, Jungersen, Kinoshita( 1 , 2 ), Kiikenthalf 1 , 5 ); Kukenthal & Gor- 

 zawsky(V), Thomson ( 3 ), and, supra p 31, Verrill ( 3 ). 



Kassianow( 1 ) describes the nervous system of Alcyonium digitatum and pal- 

 matum. The well developed nervous system of the polyps is chiefly ecto- 

 dermic, consisting of multipolar and bipolar ganglion cells, with long, very 

 fine, varicose branching processes, and fusiform sense cells the slender distal 

 ends of which project above the surface of the ectodermal epithelium. The 

 ganglion cells and their processes form a very close plexus especially on the 

 oral disc, on the oral surface of the tentacles and in the ectoderm of the distal 

 portion of the stomodseum; it ceases where the siphonoglyph begins. The aboral 

 face of the tentacle is not without nerve elements, nerve fibres are present 

 at the bases of the pinnules and some cells were found in the middle line of 

 this surface. The plexus forms a distinct nerve layer, most strongly developed 

 when the ectodermal musculature is well marked, for instance, on the oral 

 face of the tentacles and especially along the stronger lateral muscle bands. 

 The nervous system is especially well developed on the oral disc along the 

 lines of insertion of the 8 mesenteries along which the oral ends of the muscles 

 of the tentacles are inserted; the nerve fibres run parallel to one another along 

 these lines as radial nerves reaching from the mouth towards, but not 

 quite to, the edge of the oral disc between the bases of the tentacles. To 

 this point the lateral muscle bands of neighbouring tentacles converge and 

 therefore the radial nerve has probably a special significance. A feebler system 

 of nerve fibres is also present on the edge of the oral disc above the so-called 

 inter-tentacular muscle fibres. The nerve layer of the stomodseum is thicker 

 along the lines of attachment of the mesenteries than between these lines; it 

 is composed of processes of ganglion cells (like those of the tentacles and oral 

 disc) and of the proximal fibre-like branched ends of the epithelial cells of the 

 stomodseum. No nerve layer was found in the epithelium of the siphonoglyph. 

 The ectoderm of the body wall contains very large bipolar and multipolar 

 cells, with long processes, the nature of which is doubtful. Below these there 

 are other cells similar to the typical ganglion cells. In the ectoderm of the 

 body wall no nerve layer or distinct nerve tracts could be found, probably on 

 account of the absence of ectodermal muscles, no nerve cells or fibres in the 

 ectoderm of the ccenosarc, and no ganglion cells in the mesogloea, the large 

 branched mesogloeal cells having probably nothing to do with the nervous 

 system. The presence of a colonial nervous system is doubtful. Sense cells 

 are present on the oral disc and on the oral and aboral surfaces of the ten- 

 tacles in the closest proximity to the nematocyst cells. The polyps also possess 

 endodermal ganglion cells, similar to those of the ectoderm, between the muscle 

 fibres of the mesenteries. - - See also Kassianow(-). 



According to Laackmann the stomodseum of Tdesto is typically alcyonarian 



