H. B. POLLARD. 



individual tentacles, but had to relinquish it from lack of morpho- 

 logically precise observations. These tentacles may be bifid and per- 

 haps completely split, or fringed, but nevertheless all processes from 

 the skin round the mouth, e.g., those of Plecostomus may not be con- 

 sidered proper tentacles, though they may in a remote way have been 

 connected with tentacles. Such skin processes may be compared with 

 the fringe round a lamprey's mouth. 



Tentacles occur in Cyprinoids, and especially in Cobitidae, where 

 they attain an equal development with the Siluroids. They appear 

 also in Gadidae and other fish. Motella tricirrata and Mullus barbatus 

 are familiar examples. Again they ai'e found in Sturgeons, as the 

 barbels under the snout, and in the larva of an Amphibian, Dactyl- 

 ethra (Xenopus). 



Below the fish they appear in Myxinoids, and as I maintain, in 

 the well-known form of the oral cirri of Amphioxus. , 



A typical tentacle should consist of the following parts : (1) a 

 skeletal axis connected with a root piece, the axis being accompanied, 

 by (2) sensory nerves, which supply tactile organs in the skin, and 

 worked by (3) muscles belonging to a special system and not homo- 

 logous with the metameric body muscles, the (4) motor nerve supply 

 being from nerves which have been shown to arise from the lateral 

 cornu of the central nervous system, and to proceed out with the 

 sensory nerves. 



Descriptive Part. 

 Model of Auchenaspis (Figs. 1, 2, 8). 



The head of a specimen 5 cm in length, was cut in sections 30 fi 

 thick. Every second section was drawn with a camera with a magni- 

 fication of 28 (Zeiss Oc. 2, Obj. aa, height above table of drawing 19 

 cm). Thickness of wax plates 1 '35 mm. 



Model 23 cm long (or a little over 9 inches) by 20 cm broad. 



The head as far as reconstructed was about the size of a hazel nut. 

 The specimen was no doubt a young one. The replacement of cartilage 

 by bone has not occurred to any great extent. The head was not 

 modelled further posteriorly than the anterior semicircular canal. 



The anterior semicircular canal is enclosed in cartilage, which does 



