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THE " ASTERISCUS " IN FISHES. 



By Colonel C. E. Shepherd. 



Inside the skull of Teleostean fishes there are six otoliths, 

 concretions of limestone, nearly pure carbonate of lime, that 

 are contained in the membranes of the auditory labyrinth ; they 

 are placed three on each side. One, much larger than the other 

 two, is the sagitta of scientists, and is familiarly known as the 

 " earstone " or "earbone," but in the families of the Siluridee 

 (Catfishes) and the Cyprinidce (Carps), however, it is not the 

 largest, as mentioned hereafter. To the otolith that is found in 

 the "lagena" of the sacculus the name of asteriscus has been 

 given. The third stone is known as the lapillus. The lagena 

 itself, a more or less pronounced prolongation of the sacculus, 

 according to the fish to which it belongs, is looked upon as a 

 rudimentary cochlea. The asteriscus usually shows the same 

 constancy to the characteristics of the family shape as the 

 otolith known as the sagitta does. Retzius,* in his monumental 

 work on the ' Auditory Organs of the Vertebrate Animals,' 

 vol. i., gives in the plate relating to the " Lepidosteus osseus " an 

 illustration, natural size, of the asteriscus in this fish. It is a 

 little circular stone one-sixteenth of an inch in diameter, and 

 fairly circular in shape. In the plate referring to the " Amia 

 calv a " in the same work an illustration is given, natural size, 

 of its asteriscus, a rounded pear-shaped stone, three-eighths of 

 an inch in length by nine-thirty-seconds of an inch at its broadest 

 part. In another workf by the same author, in pi. iv. fig. 11, 

 he gives a drawing of the asteriscus of the Pike (Esox lucius), 

 and in pi. iv. fig. 28, a drawing of a similar stone taken from a 

 fresh- water Bream (Abramis brama). This exhausts, as far as is 

 known, the detailed illustrations of the asteriscus. The mere 

 outlines given in all the plates, with the magnified drawings of 

 the ear-membranes in all the other plates of the first work by 

 petzius, referred to above, whilst interesting as recording their 

 shapes, show nothing more than outline. The plate accompany- 



* ' Das Gehororgan der Wirbelthiere.' 

 f ' Anatomische untersuchungen, Erste Lieferung.' 

 Zool. 4th ser. vol. XIV., February, 1910. F 



