Xll 
THE VOYAGE OF H.M.S. CHALLENGER. 
upon it, an uncertainty so great that in many cases alternative schemes of genealogy are 
proposed for consideration. It may be and indeed has been argued that this uncertainty 
is inherent in all schemes of phylogeny alike, but this is an opinion which I by no means 
share. Tables of phylogeny are to the biologist what constitutional formulae are to the 
chemist, and the success in elucidating these v?^hich the latter has achieved in the face 
of opposition and discouragement, from a spirit sometimes of conservatism, and some- 
times of despair, must prove an encouragement to the biologist to persevere in his efforts 
to attain to a rational interpretation of the facts of classification. An earnest of such 
success appears to me to be furnished by Schulze’s genealogy of the Hexactinellida. 
