374 
E. RAT LANKESTER. 
which the reproductive cells develop are twenty-six in number 
on each side of the body, and correspond to twenty-six of the 
myotomes. 1 On account of the oblique shape of the myotomes 
it is not easy to decide precisely which of the thirty-six 
myotomes between the anterior snout and the atriopore are 
those to which the gonad pouches correspond. I am of 
opinion that the last gonad pouch corresponds to the last prse- 
atrioporal myotome, and this would make the first coin- 
cident with myotome No. 10, and the last with myotome 
No. 35. 
The important fact is that the gonads are affected by the 
same metamerism as that which affects the musculature. 
Occasionally specimens of Amphioxus occur in which the 
anterior one or two or the posterior gonad pouches are not 
developed, whilst the others are in full ripeness ; and in speci- 
mens taken in the autumn the entire series of gonad pouches 
are usually in an extremely rudimentary condition. 
Number of the Praeoral Tentacles. — The circular group of 
pinnate tentacles to which Amphioxus owes its earlier name 
of Branchiostoma, presents great numerical variations. The 
tentacles increase in number as the Amphioxus increases in 
size. Their first appearance is not known, but I have records 
of small individuals with twenty, of middle-sized with thirty, 
and of large individuals with forty tentacles. I am indebted 
to Dr. Hugo Eisig for kindly counting specimens of various 
sizes for me at Naples. 
The addition of new tentacles appears to take place at the 
middle point of the ventral side of the ring-like margin of the 
prseoral hood, and they are formed in pairs, right and left, the 
last formed being exceedingly small. There is no median 
tentacle, either dorsal or ventral. 
The Number of the Pharyngeal Gill-slits. — It seems from the 
descriptions given by Kowalewsky ( 11 ) that the gill-slits which 
first appear in the larva are in definite relation to the 
1 In some specimens I have counted twenty-seven, and in some twenty- 
nine ; in others again only twenty gonad pouches on one side, whilst twenty- 
six are present on the other side. 
