FLOW OF THE DEMANIAN FLUIDS 



435 



and /. (It is theoretically possible, of course, that the same tube might have 

 a flow in one direction at one time and in the opposite direction at another 

 time, but, physiologically speaking, this is an unusual occurrence, and prac- 

 tically an unheard of thing in a tubular organ "open" at both ends). We 

 may therefore eliminate from the 20 possibilities, 12 of the combinations, 

 leaving eight, acf, adf, bcf, ade, bee, bde, bdf and ace. 



But there are also two more combinations that obviously must be left out, 

 as involving physical and physiological impossibility, namely ace and bdf, 

 i.e., the cases where the three currents would simultaneously come to, or 

 radiate from, the point X; bdf, (no outlet, or reservoir), and ace, (no 

 obvious source of supply). This leaves six combinations possibly worthy of 

 discussion, acf, adf, bcf, ade, bee and bde. These six possibilities are dia- 

 grammed in figures 5 and 6. Five of these possibilities (Fig. 6) are rendered 



I. No exit pore for a; pore of uvette indicates 

 reverse of c; / doubtful because entrance of 

 sea water is possibly involved, while outflow 

 of secretion is known from lateral pores, p. 



II. No exit pore for a; f doubtful as in I; monili- 

 form glands are believed here to empty out- 

 ward because of their form and location in (). 

 fuscus; only outlet of d and / would be 

 through a. 



III. c doubtful as in I; / very doubtful as in I 



and II; the only outlet for/ and b would be If 

 through the uvette and c, reverse of direc- 

 tion indicated by structure. 



IV. No exit pore for a; the only source of a would 

 be d and the uvette. 



V. c doubtful as in I; c may also be reasoned 

 against on the basis of homologous structures 

 in O. nigrocephalalus and 0. appendicu- 

 lalum. 



Fig. 



Fig. 6. Five diagrams of supposed currents in^a demanian system, 

 h supposition are listed opposite its diagram. Compare with Fig. 5. 



Objections to 



exceedingly improbable by the physiological and morphological considera- 

 tions listed opposite their diagrams. We may therefore safely deduce, even 

 from this single discussion, that the flow is almost certainly as shown in Fig.5. 

 The significance of seven exit pores on each side in panicus (see Fig. 7) is 

 an interesting subject for speculation. It can hardly be said that the exist- 

 ence of seven pores is for the purpose of furnishing a large outlet; it would 

 seem much simpler to attain such a result by having a larger single pore. Nor 



