Introduction. 



The Tunicates which are reported in the present paper belong to the collec- 

 tions of the Svvedish Riksmuseum. They have been brought back from the Scandi- 

 navian and Arctic seas by Swedish naturalists in the course of ma ny years. A 

 survey of the Swedish scientific expeditions and voyages made before the year 1903 

 has been given by Théel in the first paper of this series (1905). 



The present paper includes northern and Arctic species of the families Styelidae 

 and Polyzoidae, of the American forms in the main only those which have been 

 brought back by Swedish expeditions. Those species which are not represented in 

 the collections of the Swedish Riksmuseum, are printed in brevier types. 



Material for comparison has been received from Professor Dr. R. Hartmeyer, 

 Berlin, to whom I am also obliged for information on several dubious forms, from Dr. 

 Nils Odhner, Stockholm, Dr. Th. Mortensen, Copenhagen, Conservator Dr. Carl 

 Dons, Tromsö, Professor Dr. L. A. Jägerskiöld, Gothenburg. 



The family Polyzoidae was established by Michaelsen in his work on these 

 Ascidians in 1900. Låter on (1904), he, and even other authors (e. g. Hartmeyer 

 1903), has subordinated the group as a sub-family to the Styelidae. In this report 

 Michaelsen's previous proposal for classification is followed: the sub-family Poly- 

 zoinae is separated from the Styelidae and looked upon as a separate family. 



From a comparative anatomical study it undeniably appears that the three 

 families Styelidae-Polyzoidae-Botryllidae form a series of closely related groups and that 

 the Polyzoidae includes intermediate forms between the Styelidae and the Botryllidae. 

 However, it seems doubtful whether a subordination of the Polyzoidae to the first- 

 mentioned family is fully justified by the reasons which have been hitherto given, 

 especially when we consider that our knowledge of the anatomy of several forms of 

 the Polyzoidae still is incomplete. Besides, the relation of the last-mentioned family 

 to the Botryllidae (and to other families) has not yet been made out. The Poly- 

 zoidae form, as is well known, a heterogenous group which shows very great diffe- 

 rences especially as regards the structure of the reproductive organs. It does not 

 seem excluded that this organ system might offer points of agreement even to other 

 families. It also remains to be decided whether some points of agreement between 

 the Styelidae and the Polyzoidae might be due to convergence or not. The importance 

 of the reproduction by budding — character which distinguishes the Polyzoidae from 



