642 
THE VOYAGE OF H.M.S. CHALLENGER. 
presentative in the Challenger collection recalling vividly that of the typical Leuconidae, 
a great stress is laid upon the close relationship of both these families in spite of the want 
of intermediate forms connecting them directly. Such being the case with regard to the 
Teichonidae, a series of illustrations are given in the Report which, beginning with the 
internal structure of one of the typical Syconidae ( Sycon arcticum), lead us gradually to 
that of one of the typical Leuconidae ( Leuconia multiformis ). The results of this 
argument are formulated as follows : — ‘ The Leu cones are nothing but modified Sy cones 
with a non-articulated tubar skeleton, their flagellated chambers are complete homologues 
of the radial tubes ; their exhalent canals owe their origin to the invaginations of the 
inner cavity, and their inhalent canals are to be regarded as homologous w T ith the 
intercanals of the Sycones.’ 
“ The author adopts the families established by Haeckel, although with considerable 
j Fig.. 218 . — Hilhardia scJmlzei, Polejaeff. 
modifications as to their diagnosis; but this is not the case so far as Haeckel’s genera arc 
concerned. As is well known, the definitions of these latter are based on spicular characters 
exclusively. Dr. Polejaeff regards this proceeding as thoroughly artificial, and comes to 
the conclusion that ‘the spicules of the Calcarea being very variable in every direction, 
could not serve as a basis for the distinction of genera, even if there were in the 
Calcareous Sponges no other characters fit for very distinct systematic definitions.’ 
The principle upon which he proceeds is the consideration of all the organs in their 
mutual correlation. Following it he distinguishes — in the family of Syconidae six genera 
[Sycon, Grantia, Ute, Amphoriscus, Heteropegma, and Anamixilla), two of which, 
namely Anamixilla and Heteropegma, are new ; in the family of Leuconidae four genera 
( Leucilla , Leuconia, Leucetta, and Pericharax) , the genus Pericharax being created for 
forms partly collected by the Challenger, partly described by Haeckel ; and as above 
