485 



Characters of use in dividing the Styelidae. 



One section of this family, namely the subfamily of the Polyzoinae, 

 was revised by Michaelsen in 1904. He based his divisions on the 

 characters exhibited by the gonads and pharynx. His revision has, I 

 think, proved to be an eminently satisfactory one. The remaining sub- 

 family, that of the Styelinae is in great need of revision. This has been 

 voiced in particular by Dr. Hartmeyer. 



I am not able to attempt this revision but I trust that the conclu- 

 sions that I have reached from the study of a small number of species 

 will be found of use when the revision is made. Certain characters that 

 appear to be of major importance have been neglected in the descrip- 

 tions of species and I desire to call attention to them. 



As in many other groups, so in the Styelidae, we have nearly every 

 possible combination of characters. This greatly augments the diffi- 

 culties of classification. Dr. Hartmeyer has expressed this difficulty 

 in his account of the family in Bronn's Tierreich in the following 

 words, »Anderseits scheint mir bei den Tethyiden (= Styelidae) eine 

 ziemlich weitgehende Konvergenz bei den verschiedensten Organen 

 vorzuherrschen , die man nicht aus dem Auge verlieren darf, und 

 die demnach bei einem Versuch die natürlichen Verwandtschaftsver- 

 hältnisse aufzuklären, eine wichtige Rolle spielt«. (Bd. III. Suppl. 

 p. 1353.) 



All classifications are admittedly artificial. But some have a 

 greater degree of naturalness than others. What rules are there to guide 

 one to the most natural arrangement of any group of organisms? There 

 are none that can be fully relied upon and at best they can be used 

 only in the most general way. The following appear to be impor- 

 tant: 



Constant characters are usually of major importance and incon- 

 stant or variable characters of minor importance. 



Fundamental (and hence primitive) characters tend to appear early 

 in ontogeny. 



Change is usually from the simple to the complex. 



An organ which is generally variable in a group is more useful 

 than one which is only slightly variable. 



The divisions that have been made in the Styelinae have been ba- 

 sed upon the characters presented by the gonads and pharynx, just as 

 in the Polyzoinae. Another feature might be added with advantage. 

 This is the condition of the atrial tentacles. They show considerable 

 variation among the Styelinae and yet the condition in each species is 

 quite constant. 



