370 
E. EAT LANKESTEE. 
pharyngeal chamber formed by the down-growth and fusion of 
the epipleural or opercular folds, is so placed that it is possible, 
by carefully tracing back the obliquely directed myotomes, to 
arrive at a definite conclusion as to its position. It appears to 
me to coincide with the 36th myotome, whilst a vertical line 
drawn from the anterior angle of the 41st myotome passes 
through its posterior margin. 
The anus coincides with the septum separating the 51st 
from the 52nd myotome, and I count ten post-aual myotomes. 
The series of numbers thus arrived at may be written thus : 
36 + 15 + 10 = 61. 1 Dr. Gunther gives four different enumera- 
tions of the myotomes of specimens of Amphioxus lan- 
ce ol at us from different localities, none of which are pre- 
cisely the same as that which I am inclined to regard as 
characteristic for Neapolitan specimens, viz. 35 + 12 + 12 = 59 
(Polperro) ; 36+14+11 = 61 (Scandinavia) ; 34+13 + 13 = 60 
(Naples); 35 + 12 + 13 = 60 (Naples). 
The Number of the Fin-Rays. — Amphioxus is provided with 
a continuous dorsal fin which reaches anteriorly below the 
extreme terminal portion of the notochord and becomes con- 
tinuous with one side of the prseoral hood, viz. the 
the right. Posteriorly the fin-like expanse is continued round 
the notochord and runs forward on the ventral surface along 
the median line, lying, however, to the right of the anus. 
Coincidently with the last twelve myotomes the fin is expanded 
both in its dorsal and ventral regions so as to form a lozenge- 
shaped caudal fin. It runs forward on the ventral median line 
as far as the atriopore. The base of the fin is supported by a 
series of fin rays which are short cylindrical pieces of a kind 
of connective tissue. The dorsal fin-rays are in a single 
series ; 2 those on the ventral surface between anus and atrio- 
1 I have also notes of countings of Naples specimens which give 
35 + 14 + 13 = 02; 35 + 14 + 12 = 61 ; 35 + 16 + 10 = 61 ; 
36 + 15 + 11 = 62. 
2 The very first fin-ray of the dorsal series is bifid at its base, as shown in 
PI. XXXYI B, fig. 11, tending to show that the ventral series are not so 
peculiar in their double character as is suggested in the text, 
