444 THE EVOLUTION OF THE METAZOA 



of neoteny (or paedomorphosis) have been looked upon by 

 many zoologists with a considerable degree of, partly justified, 

 suspicion. 



In connection with a derivation of the Chordata from some 

 larvae of the Oligomeria or even of the Tunicata, I again 

 think that such a derivation does not appear to be well found- 

 ed and that it can therefore claim little probability even if it 

 is not in principle impossible. 



First, we will mention here the attempt made by Berrill 

 (1955), whose views from our standpoint must be considered 

 as completely erroneous. Berrill's derivation starts with the 

 planktonic larvae of the Tunicata which he calls tadpoles. 

 We must above all reject the usage of this word for the plank- 

 tonic larvae of the Tunicata. These larvae are a very specific 

 form which had been developed by the Tunicata and they have 

 nothing in common with the tadpoles of the Anura, with the 

 exception that they are both larval forms that occur in the 

 Chordata. The remote external similarities can be considered 

 as pure parallelisms. 



In the Tunicata we can observe a process which we have 

 already frequently met in the Invertebrata, i. e. because of 

 their secondary transition to a sessile way of life, the Tunicata 

 developed in their ontogeny a planktonic juvenile form, a 

 larva. This certainly is a very illuminating phenomenon. Berrill 

 (1955 : 11) also considers that the Ascidia are "primarily a 

 primitive sessile, marine group of organisms." The Ascidia, 

 however, are considered quite generally and correctly, toge- 

 ther with the Tunicata, as lower Chordata which evolved into 

 secondarily sessile animals. The important problem of the 

 origin of the Tunicata is solved by Berrill very simply with 

 the following words, ". . .which may or may not be related 

 to the hemichordates." It is quite natural that Berrill who 

 derives the Vertebrata from the planktonic "tadpoles" of the 

 Tunicata does not find it interesting to try to solve the pro- 

 blem ot the origin of these Tunicata. Yet what can be done 

 if we find that it is quite improbable that any new form had 



