CHAPTER III 



THE LANCELETS Subkingdom PROTOCHORDATA 

 Class Leptocardii 



COMMON LANCELET, SINGLY, AND IN A CHAIN. 

 (Natural size.) 



WITH the curious semitransparent little creatures known as lancelets, forming 

 the only family (Branchiostomatidat) 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. 2925. First 

 described by the German naturalist Pallas in 1778, from a specimen captured on the 

 Cornish coast, the common lancelet (Branckiostoma lanceolatum) was referred to that 

 refuge for the destitute, the Molluska, where it remained till 1834, when it was re- 

 discovered by Costa, on the Neapolitan coast, who gave the name of Branchiostoma, 

 and placed it among the fishes, in the neighborhood of the lampreys and hags. It 

 was again discovered by Yarrell in 1836, who assigned the title of Amphioxus, and 

 was the first to recognize the existence of a cartilaginous vertebral column, or noto- 

 chord. 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 forward, 

 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 



(^935) 



