500 RECORD OF SCIENCE FOR 1886. 



like Protoclrili, but with dorsal chord, aud anterior respiratory diverti- 

 cula from the gut, formed the commou starting point for the Chordata. 

 In these Protochordata the jjosterior portion of the trunk is adapted 

 more especially for locomotion, while the caudal region of the ancestral 

 digestive tube has undergone progressive atrophy aud the vegetative 

 functions have become more localized in the anterior part of the trunk. 

 The transformation of one part of the segmented body of the vermiform 

 ancestors has affected all the trunk, except the cephalic extremity and 

 first segment of the body, in those forms whence the Urochordata have 

 arisen." 



(3) " The affinities between TJro- and Cephalochordata are much closer 

 than between either aud the Vertebrata." 



The manner in which the various groups have originated and the sup- 

 posed degree of their relationship are exhibited in a scheme herewith 

 presented: 



Cephalochordata. 

 Vertebrata. 



Urochordata. 



Auuulata. 



Protochordata 



Protannulata. 



(Arch, de Biol., VI, pp. 237-47G, 9 pi.; J. R. M. S. (2), 1887, pp. 

 62-05.) 



Classification of the tunicates. — The tuuicates have been variously sub- 

 divided into orders, but according to M. F. Lahille all of these arrange- 

 ments are more or less unnatural, aud in his opinion the best basis for 

 a primary classification of the class is furnished by the development of 

 the gills. "The Salpidte have a single row of holes on either side of 

 their gill organs ;" the Doliolidfe are similarly characterized, but the holes 

 are more developed as well as more numerous. The Didemnid£E have 

 three rows, and, finally, the Leptoclinidae have four. In the "higher 

 types the gill is larger, and is placed beside the intestine. In the Tha- 

 liacea the respiratory organ is very simple and without papillae." 

 Those forms, which are characterized by a simple gill, are grouped 

 together under the name " Aplousobranchiata." Those in which " the 

 gill is provided with longitudinal vessels " are grouped together under 

 the name " Phlebobranchiata." Finally, those which " have longitudi- 

 nal folds on the gills" are distinguished as " Stolidobranchiata." The 

 progressive complication of the gill, it is affirmed, corresponds "to in- 

 crease in the differentiation of the whole ascidian organism," and the 

 proposed classification, it is urged, is therefore not the outcome of de- 

 pendence on a single character, but the result of a coordination of 



