4 THE VOYAGE OF H.M.S. CHALLENGER. 



in the description of Lcucaltis clathria, 1 and yet in his system Leucetta corticata belongs 

 to one genus, Leucaltis clathria to another. In the hypothetical genealogical tree of the 

 genera of his natural system Prof. Haeckel assigns a different origin to the species 

 belonging to the same genus, as for instance, deriving the species of the genus Ascortis 

 partly from the genus Ascandra, partly from the genus Ascetta ; the species of the genus 

 Ascandra partly from Ascaltis, partly from Ascortis, &c. Nevertheless, all the species 

 of Ascortis or Ascandra are, according to him, to be united in one genus, not to be 

 divided into two or more — a direct contradiction to the description Prof. Haeckel gives 

 of his system in the words : — " constructed upon the phylogenetical principles of the 

 theory of descent (ausgefuhrt nach den phylogenetischen Principien der Descendenz- 

 Theorie "). 2 Being further obliged to acknowledge the great variability of the spicules 

 with respect to their character whether triradiate or quadriradiate, as well as the 

 inconstancy in the presence of the acerate form, Prof. Haeckel creates a new kind of variety, 

 which he calls " connexive," and regards as illustrating the transition of one genus 

 into another, and he asserts that these " connexive " varieties are " exceedingly instructive 

 for the understanding of the origin of species (hochst lehrreich fur die Erkenntniss 

 des Ursprungs der Arten" 3 ). This would indeed be very instructive, if there were in 

 the Monograph a successful attempt to prove that the seven genera of each of the three 

 families of Calcarea are really natural ; such an attempt would have been especially 

 desirable, for in some species presenting "connexive" varieties the constancy in the 

 form of their spicules is comparatively pronounced (Ascetta primordialis, Leucetta 

 primigenia), and one might come to the conclusion that the generic character is in some 

 cases more variable than that distinguishing the species. The proofs in question, 

 however, are not to be found ; the words " natural genus," " natural species," are 

 used repeatedly, and the " naturalness " of the new system is very often urged, but there 

 is only one passage in the whole Monograph which, although by no means j>roving the 

 naturalness of Prof. Hseckel's system, alludes to the manner in which its author arrived 

 at his systematic ideas. In the year 1871, on the coast of Lesina, Haeckel happened 

 to find many colonial specimens of an Ascon which was composed partly of Clathrina 

 clathrus, 0. Sch., and partly of Narcloa labyrinthus, 0. Sch., i.e., of two forms which, 

 found growing separately by 0. Schmidt, had been referred by him to two quite different 

 genera. Both the sponges grew into each other without any definite boundary, and a 

 close investigation showed that throughout the whole colony the spicules were of pre- 

 cisely the same form. 4 Oscar Schmidt, in referring his Clathrina clathrus and Nardoa 

 labyrinth us to two different genera, was guided by their external differences. The 

 discovery of Prof. Haeckel proved that such guidance is very uncertain, and so far as this 

 discovery caused him entirely to abandon the principles of classifying the calcareous sjwnges 

 previously adopted, this discovery must be called very fortunate ; but if Prof. Haeckel 



1 Kalkschwamme, BJ. ii. p. 159. ■ Loc. cit., p. 5. 3 Loc. tit., p. 23. l Loc. cit., p. 33. 



