CHAPTER XXVI 



THE TUNICATES, OR ASCIDIANS 



TRUCTURE of Tunicates.— One of the most singular 

 groups of animals is that known as Ascidians, or Tuni- 

 cates. It is one of the most clearly marked yet most 

 heterogeneous of all the classes of animals, and in no other are 

 the phenomena of degeneration so clearly shown. 



Among them is a great variety of form and habit. Some 

 lie buried in sand ; some fasten themselves to rocks ; some 

 are imbedded in great colonies in a gelatinous matrix pro- 

 duced from their own bodies, and some float freely in long 

 chains in the open sea. All agree in changing very early in 

 their development from a free-swimming or fish-like condition 

 to one of quiescence, remaining at rest or drifting with the 

 current. 



Says Dr. John Sterling Kingsley: "Many of the species 



start in life with the promise of reaching a point high in the 



scale, but after a while they turn around and, as one might 



say, pursue a downward course which results in an adult which 



displays but few resemblances to the other vertebrates. Indeed, 



so different do they seem that the fact that they belong here 



was not suspected until about thirty-five years ago. Before 



that time, ever since the days of Cuvier, they were almost 



universally regarded as moUusks, and many facts were adduced 



to show that they belonged near the acephals (clams, oysters, 



etc.). In the later years when the facts of development began 



to be known, this association was looked on with suspicion, 



and by some they were placed for a short time among the worms. 



Any one who has watched the phases of their development 



cannot help believing that they belong here, the lowest of the 



vertebrate series." 



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