“ PROBOSCIS PORES ” IN CRANIATE VERTEBRATES. 551 
journal, vol. lix, 1913). Such a conclusion is by no means 
inadmissible, but does not appear to be necessary. As a 
matter of fact no definite trace of an anterior head-cavity has 
been seen in any other group but the Selachii (adhesive 
organs apart), and it is not constant even in them. On this 
point the very careful work of Dohrn (24) seems to me 
convincing. Many authors do not admit its homology with 
a somite (v. Wijhe, Dohrn) ; rather would the walls of the 
cavity seem to be derived from the premandibular segment, 
and to represent merely a specialised region of its somite. 
If, then, the anterior head-cavity really belongs to the 
premandibular segment, and if it is represented in these 
Teleostome larvae by the adhesive organ, the remarkable 
conclusion is reached that not only in Cephalochordates, 
Selachians, and Reptiles is there evidence that the first pair 
of somites opened on the lower surface of the head (either on 
or near the hypophysial depression), but that this is still the 
case in some Teleostomes. 
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2. Bateson, W. — “Development of Balanoglossus kowalevskii,” 
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3. Chiarugi, G. — “ Di un organo epithelioli . . . di Torpedo 
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4. Dohrn, A. — “ Studien z. Urgesch. d. Wirbeltiere,” ‘ Mitth. Zool. 
St. Neapel,’ vol. xvii, 1904. 
5. Hatschek, B. — “ Studien u. Entwickl. von Amphioxus,” ‘ Arb. Zool. 
Inst. Wien,’ vol. iv, 1881. 
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