The Tunicates, or Ascidians 473 



like Appendicularia, little degeneration takes place, so far as is 

 known, the tail, with its notochord and neural chord, persisting 

 through life. 



Reproduction of Tunicates. As to the reproduction of the 

 Tunicates, Dr. Ritter writes: " In addition to the sexual method 

 of reproduction, many tunicates reproduce asexually by budding. 

 The capacity for bud reproduction appears to have been ac- 

 quired by certain simple Ascidians in connection with, probably 

 as a result of, their having given up the free-swimming life 

 and become attached and consequently degenerate. 



" Instructive as the embryonic development of the creatures 

 is from the standpoint of evolution, the bud method of develop- 

 ment is scarcely less so from the same point of view. The 

 development of the adult zooid from the simple bud has been 

 conclusively shown to be by a process in many respects funda- 

 mentally unlike that by which the individual is developed from 

 the egg. We have then in these animals a case in which prac- 

 tically the same results are reached by developmental processes 

 that are, according to prevailing conceptions of animal organi- 

 zations, fundamentally different. This fact has hardly a parallel 

 in the animal kingdom." 



Habits of Tunicates. The Tunicates are all marine, some float- 

 ing or swimming freely, some attached to rocks or wharves, 

 others buried in the sand. They feed on minute organisms, 

 plants, or animals, occasional rare forms being found in their 

 stomachs. Some of them possess a single median eye or eye- 

 like structure which may not do more than recognize the presence 

 of light. No fossil Tunicates are known, as they possess no 

 hard parts, although certain Ostracoderms have been suspected, 

 though on very uncertain grounds, to be mailed Tunicates, 

 rather than mailed lampreys. It is not likely that this hypothesis 

 has any sound foundation. The group is divided by Herdman 

 and most other recent authorities into three orders, viz., the 

 Larvacea, the Asc-idiacea, and the Thaliacea. 



Larvacea. In the most primitive order the animals are 

 minute and free-swimming, never passing beyond the tadpole 

 stage. The notochord and the nervous chord persist through 

 life, the latter with ganglionic segmentations at regular in- 

 tervals. The species mostly float in the open sea, and some 



