244 BY THE DEEP SEA. 



little purple or yellow Ascidians. It looks as though six or seven 

 of these had agreed to live together for company's sake and for 

 economy; and here we find them set in the jelly, and radiating 

 from a central aperture, the common atrial opening of the 

 colony. 



Here is a figure showing 

 part of a patch of Botryllus ^ 

 violaceus, such as you may find 

 abundant on the rocks. C 

 shows the combined tunic of 



the colony, the branchial BOTRYLLUS VIOLACEUS . 



openings, and b the common 



atrium. The general verdict on a patch of Botryllus would 

 probably be that it was some low form of sea-plant, for a 

 naked-eye view of it reveals no evidence of animal processes ; 

 yet, in spite of its vegetative condition, this in common with 

 other Tunicates is held to approach nearest to the great 

 back-boned races, the aristocracy of animal life. 



But it is a sad story of missed opportunities and consequent 

 degeneration that the Tunicates have to tell of their race. 

 Some evolutionists hold that in the primeval Ascidian we 

 must look for the progenitor of the vertebrates. We know 

 what the primeval Ascidian was like, for the form is retained, 

 according to a natural law, in the larval stage of its present- 

 day representatives. Roughly speaking, it was like a tadpole, 

 with a broad head-and-trunk combined, and a very long, 

 narrow tail, by the lashing of which from side to side it made 

 way through the waters, much as the boatman gets along by 

 sculling from the stern. At the front there was a rudi- 

 mentary mouth with three suckers, an optic organ, with 

 a retina, lens, cornea, and so forth ; an auditory organ ; the 

 promise of a well-formed brain and nervous system ; and a rod 

 in the tail might be developed into that backbone which is 

 the distinguishing mark of all the birds, beasts, fishes, reptiles, 

 and man himself. 



