ANTARCTIC SPECIES OF TEDANIA 



343 



It is of some importance to emphasize that the close resemblance of all these specimens 

 of Tedania, and the fact that they present numerous intermediates would under other 

 circumstances have suggested that all were conspecific, had the embryology not indicated 

 otherwise. In fact, had the characters of the embryos been overlooked, we should have 

 had in Tedania a similar position to that presented by Vosmaer (191 1) in his study of 

 Spirastrella purpurea (Lamarck), and (1932 et seq.) in his studies of the Porifera 

 Incalcaria of the Bay of Naples. And while I believe that Vosmaer was mainly correct 

 in his conclusions regarding S. purpurea (there are points, of course, where he has 

 obviously gone wrong), it would be better 

 to endeavour to apply the embryological 

 test as far as possible, both to this and 

 all other species. This gives to the study 

 of embryology an importance, hitherto 

 unsuspected, as the deciding criterion in 

 systematic work. 



The characters and close relationship 

 of the five species of Tedania here recorded 

 are given in the table on p. 308. 



In dealing with ^o large a collection, it 

 was found possible after a while, and once 

 the main distinguishing features were 

 appreciated, to classify specimens with 

 considerable certainty even in the absence 

 of embryos. Nevertheless, so closely are 

 these five species related and interdigitated 

 in regard to their main characters that ^. ^. , . , . , . 



1 1 1 r 11 'S- 42- Diagram showing relationships and over- 



several specimens could only doubtfully ^^^^-^^ -^ ^^e Antarctic and sub-Antarctic species of 

 be assigned to a species. Where only a Tedania. The five main areas represent types of em- 

 few specimens are found in a collec- bryology: a A, T.tenuicapitata; bB, T.c/iarcoti;cC,T. 

 tion therefore, it is conceivable that this »"^ssa;dD,Tspinata;eE 7\ murdochi a^e represent 



types of spiculation and A-D external forms of these 



difficulty will be considerably increased, ^^^^^^^ respectively. 

 unless embryos can be found in them. 



In order to stress the importance of the conclusions reached in this study of the 

 species of Tedania, it is considered worth while to express graphically the relationships 

 of these species, so that these may be contrasted and compared with the diagram given 

 by Vosmaer (191 1, p. 324) for Spirastrella purpurea (Lamarck). Vosmaer shows seven 

 groups representing typical forms of S. purpurea and indicates how these are connected 

 by intermediates. From this he concludes that the specimens comprising these groups 

 are all conspecific. In the present case, the corresponding groups are much more closely 

 connected and may be represented, not by detached circles, but by overlapping areas 

 (Fig. 42), and yet the specimens they represent actually belong to diff^erent species. 

 For example, in the area where T. niassa overlaps T. tenuicapitata may be included the 



14-^ 



