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. $49. 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 



