a —————— ee nd 
163 
lation"). It seems that this failure of so dexterous and careful an 
investigator, as F. Prarrauv was, has detained naturalists from 
making any new experiment; to my knowledge there does not exist 
in literature a communication about the respiratory movements with 
spiders. Anatomists have of course pronounced various hypotheses, 
but there is no necessity of discussing these here. 
Prarrav had discovered with certain spiders, the enlarged images 
of which he projected on a screen, very slight oscillatorical move- 
ments of the palps and the abdomen; but he did not deem them 
of any interest. I intend to explain in the first place the signification 
of these rythmical movements. 
If we examine an Zpeira that has previously been fastened at 
the thorax, under the microscope, we observe the following pheno- 
mena; the posterior point of the abdomen moves upward and 
downward with a rhythm of 130 movements a minute: they are 
slight oscillations which, though showing some diversity, are never 
smaller than ‘/,, millimeter. The entire abdomen takes part in this 
movement which forms in reality an oscillation round the peduncle 
of the abdomen. 
The paips oscillate likewise in the same rhythm, and even every 
foot, in so far as its point stands free: the angles formed by two 
successive segments become alternately larger and smaller, and so 
the point moves, as if it beat the time of the rhythm. 
One tries immediately to find the explanation of such phenomena 
in quick variations of the pressure of the blood, which would correspond 
with the systoles of the heart. The heart lies under opaque tissues ; 
but we find on the feet some spots, the teguments of which are 
sufficiently transparent to enable us to observe through them the 
circulation of the blood; we perceive in the superficial parts of the 
organ, between the muscles, ramifications of the centripetal current, 
in which the blood-corpuseles push onward by saccades that are 
isochronal with the examined rhythm. 
The contemplation of the structure of the blood-system (fig. 1) 
explains the cause of the phenomena we observed, and chiefly of 
the downward movement of the abdomen, when the heart contracts. 
1 find two factors for it: 1. the tension of the curved aorta under 
the influence of the increased interior pressure; 2. another depending 
upon the pericardial cavity: during the systole of the heart the 
pressure of the blood in this cavity decreases, and consequently this 
curved tube assumes a greater curve. 
1) F Prareau. De l’absence de mouvements respiratoires perceptibles chez les 
_Arachnides. Archives de biologie. T. VII, 1887. 
Je 
