TRANSACTIONS OF SECTION D. 715 



the European museums renders any detailed comparison with existing forms im- 

 possible, so tliat the opinions expressed in the present paper must he regarded as 

 provisional only. 



10. Some Facts and Reflections draimi from a Study of Budding in 

 Compound Ascidians. By Professor W. E. Hitter {University of 

 California). 



Numerous recent writers have doubted the genetic unily of the compound 

 ascidians ; i.e., they have doubted whether tlieir property of budding, the cha- 

 racter which all agree to be the final test of whether an ascidian is simple or com- 

 pound, has not been acquired more than once. Of these authors I may mention 

 Lacaze-Duthiers, E. van Beneden, Herdman, 8eeliger, Lahille, and Sluitei'. 



In discussing the subject van Beneden has made the apt remark that no zoolo- 

 gist would think of uniting all bud-producing actinians in one group and placing 

 them over against all others that do not reproduce in this manner. In his weU- 

 known report on the compound ascidians of the ' Challenger ' Expedition, Professor 

 Herdman not only reached the conclusion that the group is polyphyletic in origin, 

 but he also marshalled his broad knowledge to show that they probably originated 

 at three distinct points from the simple ascidians, and to show also what genera 

 trace their origin back to each of these three starting-points. The author regarded 

 this as one of the most important generalisations reached by his study of the great 

 ' Challenger ' collection. 



Quite recently M. Lahille has proposed an entirely new classification of the 

 Tunicata, in which he ignores budding as a diagnostic character of at most greater 

 than generic importance. That, however, this writer has treated the matter too 

 lightly, whether regarded from a morphological or a physiological point of view, 

 "will, I apprehend, be allowed by most students of the group. 



It is not my purpose to discuss here a classification of the compound ascidians 

 based on the hypothesis of their polyphyletic origin, but rather to show, first, 

 that they have had such an origin, and, secondl}', to consider certain developmental 

 probabilities that are involved in, or, rather, are the necessary results of, such an 

 hypothesis. 



In the interest of brevity and clearness my discussion will aim almost entirely 

 at showing that two genera of compound ascidians are, structurally considered, 

 considerably more unlike each other than each is unlike a genus of simple ascidians 

 which, in turn, are widely separated from each other. 



The genera to which I refer are rerophora and Goodsiria as representatives of 

 the compound ascidians, and Ascidia and Folycarpn as representing the simple 

 ascidians. 



Definitely stated the proposition to be established is this : Perophora and Good- 

 siria are less closely related to each other than on the one hand Perophora is to 

 Ascidia, and on the other Goodsiria is to Polycarpa. 



We will first compare the several genera anatomically, and afterwards the 

 budding in Perophora and Goodsiria ; and we may begin with Polycarpa and 

 Goodsiria. Polycarpa is closely related to Cynthia, and still more closely to 

 Styela. The genus is, however, distinctly separated from Cynthia, particularly by 

 its possessing simple tentacles and sexual organs in the form of so-called polycarps. 



Goodsiria belongs to the Polystyelidae, a small family of compound ascidians, 

 founded b}' Professor Herdman for the reception of several genera that are, as our 

 knowledge now stands, closely related to one another, and well separated from all 

 other compound ascidians, although they certainly have rather close affinities with 

 the Botryllidaj. 



The close similarity in structure between Polycarpa and the Polystyelida; has 

 been recognised by nearly all investigators who haA'e studied them, and my own 

 work has, I think, shown their kinship to be even closer than has heretofore been 

 supposed. In fact, the resemblance is so close between an undescribed species of 



