37 



interesting to mention the work of Sitovski 121). This author 

 found an acid reaction in the rectum of the catterpillars of the 

 moth, Tinea biselliella, which he fed on wool which had been 

 permeated with a solution of litmus. In the last two segments 

 a distinctly acid reaction was found. Sitovski supposed that 

 this acidity is due to uric acid. 



The question is whether we may make the same hypothesis 

 for the Echinoderms. This does not seem very probable. In its 

 favor pleads for instance the acid reaction which Roaf found 

 in the rectal coeca of the Asterids. In chapter 23 we will see 

 that these organs probably are the place of uric acid excretion 

 in the starfishes. My own findings on the PH of these organs 

 do not quite agree with his, I never found it lower than 7.3, 

 but my method is doubtlessly much more crude. The same 

 thing appears to be true for the urchin and the cucumbers 

 however ; we saw that the acidity is highest in the middle-gut 

 and decreases towards the end-gut. This does not plead in 

 favor of his hypothesis, since we will see that the acid is 

 chiefly excreted into the rectum. Moreover we must remember 

 that uric acid is an very weak acid so that it is scarcely 

 possible that in a ..buffer-mixture" like this fluid carbon dioxide 

 and a trace of phosphates are present ! it should have any 

 noticeable influence on the PH. 



The only possible explanation of the low PH which seems 

 left in this way, is the excretion of CO 2 into the gut. As a 

 matter of fact the samples described in the previous chapter 

 changed in reaction if left alone. They appeared to become 

 more and more alcaline which would prove the presence of 

 a volatile acid. 



13. TRANSPORTATION OF THE FOOD. 

 THE PERIVISCERAL FLUID. 



A definite blood system is not present in Echinoderms and 

 a special propulsatory organ is certainly lacking. Two systems 

 represent this one in this group: 1. a so-called blood-lac unar 

 system and 2. the perivisceral fluid. Opinions are different as 

 to whether these two systems communicate. Cuvier believed 

 in their communication, more recently V o g t and Yung in 

 their Lehrbuch der vergl. Anatomie (1880. Braunschweig, p. 523) 

 have defended the same opinion. H a m a n n denies it, he does 

 not consider injection experiments as convincing since the holes 

 may be caused by the force of the injection. Many other 

 investigators found elements present in the blood system which 

 are absent in the perivisceral fluid, Enriques 37) f. i. finds 

 green-red dichroitic granulae of enzymatic nature in the blood 

 system of Holothuria tubulosa, partly carried by amibocytes and 

 transported to the gut-wall by jjthe oscillations of the fluid ; 



