The Latero-Sensory Canals and Related Bones in Fishes. 465 



descriptions show that that section of the main infraorbital canal 

 that is enclosed in this bone and the squamosal, presents, in the adult 

 Menidia, the condition to which I have called attention in embryos 

 of Amia; that is, the dorsal postorbital, or postfrontal section of the 

 canal is continuous with the squamosal canal, but immediately an- 

 terior to this postfrontal canal the postorbital portion of the sensory 

 line is not enclosed in a canal. 



In Scomber there are two ante-preopercular squamosal organs, 

 both innervated by the ramus oticus, while in Menidia there is but 

 one of these organs; Scomber thus agreeing in this with Amia and 

 Lepidosteus, while Menidia agrees with Polypterus. In both Scomber 

 and Menidia, the anterior postfacial organ lies in the hind end of 

 the squamosal, posterior to the dorsal end of the preopercular canal, 

 as it does in all three of the bony ganoids above mentioned; and in both 

 fishes there is a supratemporal canal enclose in an extrascapular bone. 



In Scomber there are anterior, middle and posterior head lines 

 of pit organs; and similar lines are probably found in Menidia also, 

 for Herrick says (p. 43) that there are, in this fish, rows of naked 

 organs "which appear to correspond with the pit lines of Amia". 

 Attention may here be called to an error in the lettering in one of 

 the figures in my work on Scomber. In fig. 1 of that work the index 

 lettei'S, mi. and 2JÌ., which should refer to the middle and posterior 

 head lines respectively, have been interchanged in position. 



In Perca, Micropterus, Pomatomus, Archosargus and Cottus 

 (figs. 31 — 35) the arrangement of the latero-sensory canals is probably 

 strictly homologous to one or the other of the two slightly different 

 types represented in Scomber and Menidia, as is readily seen in the 

 accompanjing figures. The supraorbital canal, in all of them, anasto- 

 moses with the main infraorbital, the anastomosis taking place either 

 by the terminal or penultimate primary tube of the supraorbital canal, 

 which one of the two is not always evident in my sketches. In 

 all of them, the dorsal bone of the postorbital series is certainly a 

 dermal postfrontal; and the bone thus identified, in Perca, by its re- 

 lations to the latero-sensory canals, and not the sphenotic (postorbital 

 ossification), is the one to which Cuvier seems to have first given, con- 



Internationale Monatsschrift für Anat. u. Phys. XXI. 30 



