Section V, 1922 [211] Trans. R.S.C. 



XVIII. The Ascidian Family Caesiridae 

 By A. G. Huntsman, B.A., F.R.S.C. 



(Read May Meeting, 1922) 



The Caesirids [Molgulids], like so many other systematic groups, 

 are in need of a revision which will indicate relationships not only of 

 the genera, but of all the other classificatory divisions. The genus 

 Molgula, in particular, has come to include so many species that the 

 identification of a species without any delimitation of sub-genera has 

 become a matter of considerable difihculty. Postponement of attempts 

 to classify the species further only increases the confusion, since the 

 descriptions of new species are practically certain to be in most cases 

 insufîficient for subsequent assignment to sub-groups. We desire to 

 contribute toward the classification of this family, considering prin- 

 cipally those forms which we have had occasion to study. 



Nomenclature 



The International Rules of Zoological Nomenclature are the 

 result of a careful attempt by an International Committee of zoologists 

 to put nomenclature on a fundamentally just basis. The Rules have 

 received the approval of the International Congress. There is, 

 consequently, no more generally accepted guide for proper usage in 

 the naming of animals. The outstanding object in the formulation 

 of the rules has been to attain uniformity and stability. We believe 

 that this object will be achieved only by a strict adherence to the 

 rules unless and until they are changed or abrogated in special instances 

 by such general consent as approval by an international congress. 

 For these reasons we do not propose to adopt the arbitrary list of 

 "Ascidiarum nomina conservanda" prepared by Hartmeyer in con- 

 sultation with Michaelsen and Sluiter. 



Parallelism and phylogeny 



In the recent past the general aim of systematists has been to 

 produce a genetic classification, that is one, which would correspond 

 with the evolutionary history of the group under consideration. 

 It has been taken as axiomatic that relationship proves community 

 of origin. In the inorganic world we do not hold to this view. It is 

 a commonplace that substances to all intents and purposes identical 



