292 TADPOLES OF THE SEA 



endowments compared with what he was. His eyes are 

 large and keen in sight ; his hearing organs are large and 

 good ; so are his organs of smell ; and he has a very fine 

 tongue, which he can shoot out, so as to pick up quickly 

 a fly or spider and draw it into his mouth. 



Starting from a stage of their tadpole life, when they 

 are practically equal in powers and endowments, the frog 

 has progressed, whilst the Ascidian has retrogressed. The 

 frog has become more complex than he was as a tadpole, 

 more varied in his powers ; the Ascidian has become less 

 complex ; in fact, simplified, and with a less variety of 

 powers than when it was a tadpole. Both the Ascidian 

 and the frog exhibit, as all animals do in their growth 

 from the egg, a more or less blurred recapitulation of the 

 long line of ancestors through which they have developed 

 from a unicellular animalcule. The tadpole is a recapitula- 

 tive presentation of the fish-like ancestor common to both 

 the common Ascidian and the common frog. It is em- 

 phasised and of some duration in their growth from the 

 egg, but in other closely allied Ascidians and frogs, and 

 in most other vertebrates, the tadpole stage is blurred 

 and lost. The inert sac-like Ascidian into which the 

 Ascidian tadpole is converted, though it has a very 

 wonderful trellis-like gullet and a stout, tough coat to 

 protect it, is yet a " poor creature," as compared with 

 the frog a helpless, passive lump, living on the abundant 

 microscopic particles of food obtained from endless pints 

 of sea-water, to the mechanical straining off of which from 

 the ceaseless stream passed into its mouth and out of its 

 branchial pore it is comfortably and irretrievably aban- 

 doned. This is its speciality. Its apparatus for this one 

 process is highly perfected, but in every other respect the 

 Ascidian is simplified and negative as compared with its 

 tadpole. 



The descriptive term " degeneration " has been applied 



