91 
1916-17.] Experiments and Observations on Crustacea. 
limbs, etc.) are almost impossible to explain on the Darwinian hypothesis. 
Moreover, to the school of “ developmental mechanics ” we owe demonstra- 
tion of the fact that in ontogenetic development there is an early stage 
“ during which each cell is pursuing the proper course predetermined 
by its own inherent qualities ; and that to this there succeeds a stage 
in which the interference of the general functional activity of the organism 
is necessary to the completion of the process.” 
In this connection consider the correlation in phylogenetic development 
of the fore- and hind-limb of higher vertebrates. Here we have to 
assume either that the moulding influence of the environment was very 
direct, or then that on the one hand there existed some co-ordinating 
communication, implying “ interference of the general functional activity 
of the organism,” between the fore- and hind-limb, or on the other that 
the unfolding impulse (with its material substratum) pursued a course 
predetermined by inherent qualities. 
When, again, we compare the reptant peracaridan with the reptant 
vertebrate flexion-complex and limb-taxis, we see a correlation. It is 
far less precise in detail than that between the two vertebrate limbs, but 
nevertheless sufficient to excite wonder. Here there is no “ co-ordinating 
communication ” between the two respective unfolding impulses (with 
their material substratum); there is either predetermination or then the 
influence of the environment is direct. 
These specific cases have been reintroduced to show that by 
deliberately selecting examples of homoplasy in non-homogenetic organs 
it may be possible to carry out investigations parallel to the ontogenetic 
experiments of the school of developmental mechanics — and with this 
advantage in the case at least of the “ serial homologies,” that one gets 
rid of any possible co-ordinating communication between the unfolding 
impulses (with their material substratum). One may thus study, as it 
were, the direct action of the environment. In this connection compare 
Henderson (1913). 
I have here striven to make out a case for the systematic study of 
the homoplasies or analogies as opposed to that of the homogenies. 
Physiological study of the invertebrates suffers at present from a certain 
indefiniteness and scatteredness of aim. We are not without books on 
“ comparative physiology.” It is no discredit to the writers that they have 
difficulty in deducing principles and generalisations. It is the peculiar 
fortune of the physiologist to view the great achievements of morphology, 
to know that his science is directly and intimately involved, and yet to 
be unable to point to any great unifying physiological generalisation 
