The Reaction to Tactile Stimuli 
261 
ver}/ young fish. Quite conceivably, the swimming movement 
might become modified during growth, in response to changes in 
body form, modes of feeding and other factors of behavior; and it 
is still quite possible that in the adult fish there is a cephalo-caudal 
progression of movement which is obscured by other factors of 
special adaptation. 
This contribution should not be submitted without reference to 
the splendid work of Paton^ on the reaction of vertebrate embryos. 
This is the only paper accessible to me that bears in any respect 
immediately upon the work in hand. Paton's contribution, how- 
ever, is chiefly upon the development of fishes, with merely a refer- 
ence to Rana and Amblystoma, and is particularly devoted to the 
spontaneous movements. Such movements would seem to be much 
more common in embryos of fishes than in embryos of Diemyc- 
tylus. The latter, during the early phases of irritability to touch, 
may be under observation for hours without making a perceptible 
spontaneous movement of the trunk, cardiac and branchial move- 
ments not being taken into account in my work. 
My approach to the problem of physiologico-anatomical correla- 
tions in the development of the neuro-muscular system of verte- 
brates differs materially from that of Paton’s method. Paton 
undertakes “to determine in a general, but not in a specific way” 
how far the reactions are dependent upon “the functional activity 
of a nervous system” and dismisses the study of specific reactions 
as impracticable, on account of the “apparently conflicting” data; 
but my work clearly demonstrates that, in response to the stimulus 
employed in my experiments, embryos of Diemyctylus have a very 
definite and regular mode of response, during certain phases of 
development. In fact I have yet to find the first individual that, 
through any considerable period, reacts contrary to the mode 
described in this paper, that is to say, no embryo has yet come 
under my observation that regularly moves its head toward the side 
touched when the stimulation is on the head. Nor have I found a 
single embryo that, observed for a considerable period, has not 
fallen under one of the three types which I have here described. 
^The Reaction of the Vertebrate Embryo and the Associated Changes in the 
Nervous System. Mittheilungen a. d. zoologischen Station zu Neapel, Bd. 18, 
Heft 2 u. 3, 1907. 
