365 



had found in Amia was true, in principle, for all fishes, I sought in 

 infraorbital, as opposed to supraorbital, a proper name for the whole 

 canal; for, aside from the fact of its development as a continuous whole, 

 I considered it of great descriptive convenience to treat Li as such, 

 and to give to the sense organs along it a serial numbering. 



The possibility of the supratemporal cross-commissure representing 

 the true anterior end of that part of the canal that belonged to the 

 body was considered by me at the time, and is indicated in my state- 

 ment (No. 1, p. 499) that there are forty organs in all on each side of 

 the head of Amia. Referring to this particular statement Cole says 

 (No. 6, p. 181) that it "is doubtless a miscalculation, since the numbers 

 he gives total 47". It was, on the contrary, not a miscalculation, but 

 perhaps an incomplete statement, for I did not duly consider the pos- 

 sibility of the extrascapular, and the other, more posterior bones, which 

 together lodge the remaining seven organs of the total count, being 

 considered as parts of the skull. I considered them all, with Sagemehl 

 (No. 23, p. 48 and 107), as, unquestionably, parts of the secondary 

 shoulder girdle. 



Nevertheless, notwithstanding the fact that the extrascapular was 

 thus considered as belonging to the body rather than to the head, the 

 possibility of the supratemporal commissure representing the true an- 

 terior end of the lateral canal of the body was rejected for several 

 reasons. The most important of these reasons was that the commissure 

 in Amia seemed to me to represent a partly enclosed line of pit organs, 

 formed at right angles to the line of the main canal; and that this line 

 of pit organs was similar in every respect to the middle head line of 

 pit organs found opposite my organ 17 infraorbital, to the dorsal body 

 line found opposite my organ 20 infraorbital, and to the pit lines found 

 in connection with most of the organs of the lateral line of the body 

 as far back as the investigation was carried. 



The commissure in Amia thus seemed to me to be one of a set of 

 serial formations, occupying, perhaps, a metameric position. I had, how- 

 ever, no sufficient proof that it was such, and, accordingly, thought best 

 not to attempt any special discussion of it. Since then I have seen 

 nothing, either in my own work or in that of others, that warrants the 

 forming of a definite opinion regarding it, either one way or the other. 

 Platt's work on Necturus (No. 18), however, seems decidedly to favour 

 the supposition that it is both serial and metameric; while Mitrophanow's 

 work on Selachians (No. 16, p. 207) tends to show that, if not serial 

 and metameric, it is, at least, a line that develops from a detached or 

 separate center, and that it has the same measure of independence from 

 the main sensory line that the several pit lines of Amia have. Cole's 

 work on Chimaera (No. 5), on the contrary, might be taken to indicate 

 that it is the true anterior end of the lateral canal of the bod} T ; and 

 that Cole considers it as such is certainly indicated both in the num- 

 bering he adopts for the organs in the canals in Gradus, and in a pas- 

 sage on p. 122, which contains the assertion, that the commissure "should 

 form a dorsal connection between the anterior extremities of the 

 lateral canals''. As the words "anterior extremities" are there italicised 



Anat. Adz. XV. Aufsätze. 25 



