446 RECORD OF CURRENT RESEARCHES RELATING TO 



Echinodermata. 



Buccal Skeleton of the Asterida and Ophiurida.* — This is 

 another of Dr. Ludwig's interesting contributions to the morphology 

 of the Echinodermata ; it is primarily directed against the views put 

 out by M. Viguier.f Both authors have, however, in view the same 

 object, a desire, namely, to refer the parts of the buccal skeleton to 

 definite parts of the arm, and the essential difference between them 

 appears to Dr. Ludwig to lie in this : Viguier considers that four pairs 

 of skeletal pieces, two ambulacral and two adambulacral, are to be 

 found in the buccal skeleton ; Ludwig thinks that only three pieces, 

 two ambulacral and one adambulacral, enter into the composition of the 

 same parts. The view of the former is based on the following facts, 

 or supposed facts : — As every pore for the ambulacral suckers is in 

 the arm bounded by four skeletal pieces, two ambulacral and two adam- 

 bulacral, the same arrangement must obtain around the mouth. On 

 the other hand, Ludwig holds that every ambulacral pore is, as a rule, 

 bounded only by three pieces, namely, by two successive ambulacral 

 pieces, which form the median, aboral, and adoral margins, and an 

 adambulacral piece, which closes the pore laterally. If this view be 

 correct, and it is one that is supported by anatomical and embryo- 

 logical investigations, it follows that Viguier's view is not supported 

 by facts, and must therefore fall. 



A further doctrine supported by the French anatomist is that the 

 process and body of the " tooth " are, morphologically, of the same 

 series as the adambulacral pieces; here again, Ludwig takes the 

 directly opposite view, and says that they belong to the ambulacral 

 set, and this view he bases on the following considerations : — (1) The 

 muscular connection between the two " dental processes " has the same 

 disijosition as the lower transverse one of the ambulacral groove which 

 connects together the two ambulacral pieces of the same pair ; the 

 view that this muscle is specially developed in the peristomial region 

 is a corollary of the doctrine that the " dental process " belongs to the 

 adambulacral series. (2) In young star-fishes the first ambulacral 

 pieces are not distinct, but articulate with one another in the median 

 plane, just as do all the other pairs of ambulacral pieces. 



The author proposes to give the name of " ambulacral skeletal 

 segment " to the skeletal pieces, which are set around the radial water- 

 vessel, and are arranged in successive groups ; each of these consists 

 of two ambulacral, and of two adambulacral pieces. In the Asterida 

 these parts take on the following characteristic arrangement around 

 the mouth : the whole of the first skeletal segment and the ambulacral 

 pieces of the second become more firmly united, and are converted 

 into the parts of the buccal skeleton. Ctenodiscus is remarkable for 

 having this arrangement extended to a further set of each series. 



Passing over the other points in controversy between these writers, 

 we come to Ludwig's account of his examination of the dry specimens 

 of Astroplnjton arhorescens. Confirming on the whole the views of 

 Johannes Miiller, he directs attention to an interesting, and as yet 



* ' Zeitschr. wiss. Zool.,' xxxii. (1880) p. G72. 

 t See this Journal, ii. (1879) p. 428. 



