104 



THE ZOOLOGIST. 



not fully explain the vital properties, for instance, of living 

 protoplasm, viz. the heredity and adaptivity of Prof. Allman, 

 notwithstanding all the labours of Weismann and Semon. 

 Haeckel, however, holds that all living plasm has a psychic life, 

 but that the higher psychic functions, particularly the pheno- 

 mena of consciousness, only appear gradually in the higher 

 animals. 



Prof. Francis Darwin, again, insists that the dim beginnings 

 of habit or unconscious memory in the movements of plants and 

 animals must have a place in morphology, and in his able and 

 ingenious Presidential Address to the British Association he 

 concludes by stating that the mnemic hypothesis of Evolution 

 makes the positive value of Natural Selection (which has 

 been taunted with being a negative power) more obvious. 

 There can be no doubt that memory goes far down in the 

 animal scale. 



Special difficulties present themselves to the investigators 

 of complex groups, for example, the Polychaete Annelids and 

 Starfishes. In the former it is hard to decipher the ways of 

 natural or other selection in the marvellous general variety, yet 

 individual fixity of structure in the bristles and hooks. For 

 instance, in such forms as Harmothoe, not only do the bristles 

 in front differ from those in the rear, but the dorsal and ventral 

 divisions of each foot present a characteristic variation from the 

 upper to the lower edge of each fascicle. Moreover, every 

 member of each species shows precisely the same variation 

 anteriorly and posteriorly, and from the dorsal to the ventral 

 border of each division of the foot. Further, a single bristle or 

 hook of almost every species of annelid retains its characteristic, 

 structure from generation to generation, so as to be a key to the 

 species. Nevertheless, it occasionally happens that two forms 

 come so near each other that it is hard to decide as to specific 

 identity or difference. 



In regard to the latter (Echinoderms), the younger Agassiz, 

 confining his remarks for the moment to the Sea-urchins, stands 

 aghast in calculating the possible combinations that can be 

 produced by the modifications of ten of the most characteristic 

 features. He is of opinion that the making of a genealogical 

 tree is a hopeless task. 



