550 
EDWIN IS. GOODRICH. 
Postscript. 
Since this paper was printed I have again come across 
some interesting work which had unfortunately escaped my 
memory, but to which attention must be drawn, as it has an 
important bearing on the questions dealt with above. I refer 
to the papers on “ Amia” by Phelps / Science/ vol. ix, 1899), 
by Reigliard and Phelps Journ. of Morph./ vol. xix, 1908), 
and by Eycleshymer and Wilson (‘ Biol. Bull./ vol. xiv, 1908), 
and on “Polypterus” by Kerr /Budgett Mem./ 1907). 
These authors trace the development of the adhesive or 
•cement organ of the larva from paired diverticula of the 
anterior end of the archenteron. Each diverticulum becomes 
nipped off, and subsequently acquires an opening to the 
■exterior. The adhesive organs of Lepidosteus and Acipenser 
are probably of the same nature. Now, while Kerr is un- 
willing to commit himself to any theory of the homology of 
these organs, but nevertheless indicates “ the probability that 
they correspond with the premandibular heud - cavities,” 
Reighard and Phelps definitely compare the pouches which 
-give rise to the adhesive organs to the so-called anterior 
head-cavities found by Miss Platt in Acanthias, and supposed 
to represent a pair of somites in front of the premandibular 
somites of Balfour. Following Neal /Bull. Mus. Comp. 
Zool./ vol. xxxi, 1898) they further homologise these anterior 
head-cavities with the first pair of somites in Amphioxus (the 
left one of which opens to the exterior), and suggest that they 
and the adhesive organs may be homologous. This com- 
parison, however, raises a serious difficulty. If the anterior 
head-cavity really represents a separate segment, then the 
segmental correspondence between the first pair of somites in 
Amphioxus and the premandibular somites in higher verte- 
brates would seem not to hold good. Since no somite has 
been found in Petromyzon in front of the premandibular, we 
may be forced to the conclusion that the whole cephalic 
structure has been transposed one segment back in the 
<Grnathostomata (see “ Segmentation and Homology,” this 
