CHAPTER III, 
The Lancelets, — Subkingdom PROTOCHORDATA 
Class Leptocardii. 
COMMON LANCELET, SINGLY, AND IN A CHAIN ( nat. size). 
With the curious semitransparent little creatures known as lancelets, forming 
the only family (. Branchiostomatidce ) and genus of the class to which they belong, 
we leave the Vertebrates and come to the lower group of Protochordates; all of 
which retain the three essential vertebrate features mentioned on p. 549. First 
described by the German naturalist Pallas in 1778, from a specimen captured on 
the Cornish coast, the common lancelet ( Branchiostoma lanceolatum ) was referred 
to that refuge for the destitute, the Mollusca, where it remained till 1834, when it 
was rediscovered by Costa, on the Neapolitan coast, who gave the name of 
Branchiostoma, and placed it among the fishes, in the neighbourhood of the 
lampreys and hags. It was again discovered by Yarrell in 1836, who assigned the 
title of Amphioxus, and was the first to recognise the existence of a cartilaginous 
vertebral column, or notochord. The upper figure of our illustration shows the 
pointed extremities of the body, and also a number of chevron-shaped lines, with 
their angles directed forwards, these being the partitions dividing the longitudinal 
mass of muscle clothing each side of the body into a series of segments. And it is 
due to this segmented structure that the lancelet is enabled to swim so speedily as 
it does, its progress being effected by serpentine movements of the body. Paired 
fins are wanting; but the back is provided with a continuous dorsal fin, expanded 
posteriorly into a caudal fin, and continued forwards to join the ring of feelers, or 
