INVERTEBKATA, CRYPTOaAMIA, MICROSCOPY, ETC. 737 



organs of the Teleostei as having a similar function, while there 

 appears to be a general consensus of opinion that the similarly shaped 

 (goblet-shaped) organs, which are found again on the tongue of the 

 Mammalia, are entrusted with the duty of tasting organs. 



Echinodermata. 



Anatomy of the Ophiurida.* — Dr. Ludwig deals in this paper 

 chiefly with the skeleton and with the generative organs of the Brittle- 

 stars ; pointing out the extreme difficulty offered by them, he says 

 that he has busied himself chiefly with the, in all respects, largest form 

 known to him — Ophiarachna incrassata Miiller and Troschel, which 

 came to him from Cape York. 



Before considering their relations to the Asterida, he deals with 

 the leading characters of their own skeleton. In an arm, four dif- 

 ferent kinds of skeletal structures may be made out — the jointed 

 plates, the lateral, the ventral, and the dorsal shields. The last are 

 almost completely rectangular, are three times as broad as they are 

 long, at the base of the arms, and they occupy nearly the whole 

 of the dorsal side ; the lateral plates carry the four rows of spines 

 and the tentacular scales, while the ventral plates are quadrangular, 

 and have a somewhat convex aboral edge ; on their adoral edge there 

 is a process with a depression on either side. The joints, which are 

 formed by the fusion of two lateral pieces, are, with the exception of the 

 first pair, intimately connected ; in form they are discoid and pre- 

 sent four surfaces ; in the centre of the adoral and of the aboral 

 surface there are protuberances and depressions by which the several 

 joints are connected together. On the adoral side we find superiorly 

 two lateral cavities, and, inferiorly, a median one, while superiorly 

 there is a median protuberance, and inferiorly two lateral ones: 

 on the aboral side the conditions are reversed. In addition to 

 these there are other cavities which are less evident, and which go to 

 make up four for either side of each joint. The arrangement is, on the 

 whole, of such a kind that movement is possible in a horizontal as 

 well as in a vertical plane. Eunning along the median ventral line 

 of the arm there is a groove, at the base of which are small orifices, 

 which lead into five canals that traverse the joints. The adoral one 

 serves for the entrance of a nerve, and the aboral ones for a branch of the 

 ventral water-vessel ; and it is of interest to note that the arrangements 

 of this last-named system point, in the opinion of Dr. Ludwig, to the 

 complete homology of the joints of the Ophiurid and of the Asterid 

 arm. This view, which was held by Meckel and by Johannes Miiller, 

 has been lately opposed by Gaudry and by Lyman ; but it is impos- 

 sible to enter into a detailed description of the question here, and we 

 can only say that the lateral shields of the Ophiurida are regarded by 

 Dr. Ludwig as being homologous with the adambulacral plates of the 

 Asterida, while the ventral shields of the former should be regarded 

 as subambulacral plates, which are absent in the Asterida. 



As to the skeleton of the oral region, it is thought that the ambu- 

 lacral covering-pieces are parts of the ambulacra, the lateral oral 



* ' Zeitschr. wiss. Zool.,' xsxi. (1878) p. 348. 



