270 THE STUDY OF ANIMAL LIFE CHAP. 



the pharynx, are very complicated as compared with 

 their condition in the larva ; the young Tunicate is a 

 Vertebrate, the adult is a nondescript. 



Tunicates are hermaphrodite a very rare condition 

 among Vertebrates ; some of them exhibit ' alternation 

 of generations," as the poet Chamisso first observed ; 

 asexual multiplication by budding is very common, and 

 not only clusters but more or less intimate colonies are 

 thus formed. A few are free-swimming, such as the fire- 

 flame (Pyrosoma), a unified colony of tubular form, some- 

 times 2 or 3 feet in length, and brilliantly phosphorescent. 

 Very beautiful are the swimming chains of the genus 

 Salpa, whose structure and life -history alike are com- 

 plicated. 



3. Lancelets. The third step on the Vertebrate 

 ladder is occupied by the lancclets or Cephalochorda 

 (Amphioxus and two or three other genera). They are 

 fish-like in form, about two inches in length, and are 

 widely distributed on the sandy coasts of warm and 

 temperate seas. They live rather sluggishly in fine sand 

 and feed on microscopic organisms and particles wafted 

 into the mouth. 



From tip to tail of the translucent body runs a support- 

 ing notochord ; above this is a spinal cord, with hardly 

 a hint of brain. The pharynx bears a hundred or so gill- 

 slits, which in the adult are covered over in a rather 

 complex way, so that the water which enters by the 

 mouth finds its way into an atrial chamber, as in Tuni- 

 cates, and thence out by a single aperture towards the 

 posterior end. Although Amphioxus has no skull, nor 

 jaws, nor brain, nor limbs, it deserves its position near 

 the base of the Vertebrate series. The sexes are separate, 

 and the eggs are fertilised outside of the body. The 

 development of the embryo has been very carefully 

 studied, and is for a time very like that of Tunicates. 



4. Round - mouths or Cyclostomata.- -The hag-fishes 

 and the lampreys and a few allied genera must be excluded 

 from the class of fishes. They arc survivors of a more 

 primitive race. They are jawless, limbless, scaleless, 

 and therefore not fishes. 



