MODERN BIOLOGY 509 



theory and endeavours to find a primal form from which the rest of the 

 Radiolaria could be derived. On the whole, however, the system was set 

 up in the traditional way. 



Later on Haeckel continued the work on the Radiolaria, adding two 

 new parts (1887-8), and in the special section of these he describes several 

 hundred new species, which are splendidly illustrated. The complaint has 

 been made against his descriptions that they keep too much to the skeleton, 

 and against the illustrations that they are over-simplified, but on the whole 

 both text and illustrations compare creditably with the former volumes of 

 the work. The general section of the new work, on the other hand, is strongly 

 characterized by the natural-philosophical speculations which Haeckel had 

 produced in the mean while, and to which we shall revert later on. 



His work on sponges 

 Another field that Haeckel made the subject of systematic research was the 

 sponges, of which he dealt especially with the Calcarea in his monograph 

 Die Kalkschwdmme, of 1871. In this work he has recorded his most consist- 

 ent attempt to create a Darwinistic classificational system — a true "nat- 

 ural" system based on descent, instead of the old "artificial" system. The 

 group had been very little investigated and the facts contributed by Haeckel 

 are of some importance, considering the age when they were published, al- 

 though they have, of course, undergone a good deal of modification as a 

 result of subsequent research. On the other hand, this natural system has 

 its curious features. The order of the Calcarea is divided into families ac- 

 cording to the shape of the canals in the walls of the sponge, and this mode 

 of classification has been retained by subsequent naturalists. The division 

 into genera, on the other hand, is based on the calcareous spicules of the 

 skeleton. These two features, the canals and the calcareous skeleton, are, ac- 

 cording to Haeckel, the only systematically employable elements, for their 

 form is inherited, whereas the artificial system has taken account of mouth 

 formation and colony or solitary life, which are dependent upon "adapta- 

 tion." No evidence, however, is offered in proof of these statements, and 

 it certainly does seem decidedly artificial to base the division into genera 

 upon one single character, without the slightest attempt to test the theory 

 by means of comparative morphology. Nevertheless, the system has its pe- 

 culiar interest as an attempt to separate entirely from the Linnasan system. 

 The terms hitherto employed have been entirely abolished; instead of " gen- 

 era" he uses "generic varieties," besides which there are differentiated and 

 nominated "specific, connective, and transitory varieties" or "initial, bind- 

 ing, and transitional species." One must admit the logical consistency of 

 this attempt to get away from Linnasanism; the latter rests entirely upon 

 the immutability of the species, and if it is once denied, it is necessary really 

 to set up a new system with a different idea of species. Haeckel's attempt. 



