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The Arrangement of the Tentacles. Since Fischer discovered (1889) in C. 

 membranaceus the existence of an unpaired tentacle corresponding to the ventral siphonoglyph, 

 various attempts have been made to formulate a definite arrangement for the marginal and 

 labial tentacles. Although in their details these attempts have produced somewhat discordant 

 results, vet they have shown that the tentacles of the Cerianthids cannot be regarded as being 

 arranged in cycles comparable to those of the Actiniaceae; that, however, cycles of another 

 type can be made out; that the corresponding tentacles of the marginal and labial sets do 

 not necessarily belong to corresponding cycles; and that the tentacles of the various quartette 

 groups are, in general, defmitely and similarly arranged with regard to the cycles. 



One of the discrepancies noticeable in the different observations is the number of cycles 

 recognized. Thus, Fischer (1889) recognizes but three, while Cerfontaine (1891), Faurot (1895) 

 and Carlgren (1900) admit four in each set, and van Beneden (1898) recognizes in C. lloydii 

 three in the marginal and four in the labial set. The difference is, however, of comparatively 

 little importance, since the two outer cycles are somewhat crowded together and differences of 

 contraction will readily lead to confusion of the two. In the examples of P. fimbriatus which 

 I have studied there are four cycles in each set, but here and there, at different portions of 

 the circumference, it is difhcult to determine whether a tentacle belongs to the third or the 

 fourth cycle, especially in the case of the marginal set. 



The differences observed in the arrangement of the tentacles in the various cycles are 

 of greater importance. The arrangement which Faurot (1895) figures for the marginal tentacles 

 of C. incmbraiiacetLS may be represented thus: 



— 1 | 4, 2, 3, 1 | 4, 2, 3, 1 |J 3, 4, 1, 4, 3 |j 1, 3, 2, 4 | 1, 3, 2, 4 | 1 -, 

 a formula which represents the protocnemic tentacles and two quartettes on either side, and 

 which may better be represented thus; recognizing the fourth tentacle from the mid-ventral 

 line as belonging to the protocnemic set; 



— 1, 4, 2, 3 | 1, 4, 2, 3 || 1, 3, 4, 1, 4, 3, 1 ; | 3, 2, 4, 1 | 3, 2, 4, 1 -. 

 Earlier, however, Cerfontaine (1891) had found the arrangement to be as follows : 



'i ji -i 4 I 'i ji J '4 l i ji 4i -1 4i 01 ' | 4i -1 Ji L | <+> -1 01 l 1 



the difference arising from a confusion of the third and fourth cycles in the quartette tentacles 

 and of the first and second in the protocnemic ones. Carlgren (1900) confirmed Cerfontaine's 

 results and found the same arrangement in C. lloydii, in which form van Beneden (1898) had 

 described the arrangement as 



3i 2 > j> ' | 3' 2 i ji l | 2 > o> 2 i 01 - 'iji-i j | x i ji -1 3 

 which may be better expressed thus : 



1 1 Ji -i J I l ! 0> -1 | 'i -1 Ji -1 Ji -1 ' | J) 'i Ji ' | J) -1 J' * 



The difference is explicable, so far as the quartette tentacles are concerned by the fact that 

 van Beneden recognized only three cycles in the marginal set of tentacles; there is, however, 

 a discrepancy in the arrangement of the protocnemic tentacles. In C. solitarius Carlgren found 

 the same arrangement as in the other forms, although the third and fourth cycles are less 

 clearly distinguishable and irregularities, due to the failure of tentacles to develope, occur. 



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SIBOGA-EXrEDITIE XV a. 3 



