26 Coelenterata. 



Carlgren( 3 ) describes Arachnactis lobiancoi [see also above p 25], taken in 

 the plancton at Naples. The column was, when extended, 21 mm. long and 

 10 mm. broad, the marginal tentacles 18 mm. long and the oral tentacles 4 mm. 

 There are 16 marginal tentacles 7 to the left and 8 to the right of the 



directive tentacle, and 17 oral tentacles - 8 on each side of the directive 

 tentacle. The stomodseum is about half the length of the body; the siphono- 

 glyph is very deep, and is continued at a hyposulcus, which is nearly one 

 fourth the length of the body. The ectoderm of the column- wall is very 

 thick, and contains numerous nematocysts with coiled threads, and also thick- 

 walled and a few thin-walled nematocysts. The layer of nerve-fibres and 

 ganglion-cells is well developed. The longitudinal muscle-layer is thick in the 

 middle of the body, but becomes thinner at the ends. The endoderm of the 

 body-wall is thinner than that of the mesenteries and than the ectoderm; it 

 contains, here and here, thin-walled nematocysts, but these are much more 

 numerous in the endoderm of the mesenteries (especially in the aboral portion) 

 and in the acontia [see above p 25,. The ectoderm of the tentacles is 

 thick, and contains 5 sorts of nematocysts; the mesogloea and endoderm in the 

 tentacles are thin. The ectoderm of the stomodaeum is high, the longitudinal 

 musculature weak, the mesogloea thin, and the endoderm like that of the 

 body -wall. The ectoderm lining the siphouoglyph and hyposulcus consists 

 chiefly of large supporting cells, and nematocysts are rarely present. There 

 are 17 mesenteries; the directives are long and do not bear mesenterial fila- 

 ments. Protomesenteries 2,2 are the longest, and bear ciliated tracts and cnido- 

 glandular tracts, the former being about 3 times as long as the latter. Proto- 

 mesenteries 3,3 are distinctly shorter; their ciliated tracts are very short, but 

 their cnidoglandular tracts are long. Metamesenteries 1,1 are almost as long 

 as protomesenteries 2,2, and the ciliated region extends along almost the whole 

 of the mesentery; at the lower end each bears an acontium. As is usual 

 in Cerianthids, the metamesenteries 1, 3, 5 have long ciliated tracts, while 

 2, 4, 6 have very long cnidoglandular tracts and very short ciliated tracts. 

 The structure of these tracts is described in detail. The mesenterial muscu- 

 lature is weak, and recognisable only in the oral region. The endoderm of 

 the mesenteries is thick and vacuolated. Gonads were not yet developed. The 

 author also describes the marginal and oral tentacles, the stomodseum, siphono- 

 glyph, hyposulcus, mesenteries and acontia of Cerianihus membranaceus, 

 Pachycer. solitarius and Arachnanthus oligopodus. He concludes that A. lobi- 

 ancoi is nearly related to Arachnanth. oligopodus, and is probably referable 

 this genus. He appends a description of the principal features in the structure 

 of Pachycerianthus mana. See also Colgan( 1 ). 



Vaughan( 1 ) has continued his observations on the rate of growth of corals 

 [see Bericht f. 1911 Coel. p 25]. Planulse which became attached to tiles in 

 the laboratory, in June 1910, were placed in the sea. Those of Favia 

 fragum had given rise during the 12 months to colonies varying in height 

 from 4 to 6 mm., in greater diameter from 13 to 20 mm., and in lesser dia- 

 meter from 12 to 18 mm., and consisting of 9 to 18 calices. 12 planulae of 

 Porites astreoides had given rise to 7 colonies, each 2 to 3 mm. high; the 

 largest was 23x14 mm. in diameter, and was probably formed by the fusion 

 of colonies from 6 planulse; the other colonies, each derived from a single 

 planula , varied from 4 to 10 mm. in diameter. 8 tiles bearing polyps of P. 

 a., derived from planulse which had fixed themselves to the tiles in aquaria, 

 were placed in the sea. At the end of a year the diameters of the corals 

 derived from single planulse varied from 7x5 to 19 x 18 mm. The strong 



