133 321 



Floscnlaria and Hi]datina. Only rarely (Asplanchna) have two different kinds of 

 lateral canals on each side been observed. As far as I have been able to observe, 

 the vibratile tags are commonly implanted directly upon the glandular tubes, the 

 capillary tubes being often absent; upon this point more thorough observations are 

 however necessary. Even if the excretory organs are overlooked in many cases owing 

 to the smallness of the organisms, there can be no doubt that they really do not 

 exist in many of the smallest and most reduced males. This is the case with the 

 males of Conochilus, Notholca acuminata, Pompholijx sulcata, Polijavthra platijptera, 

 Gastropus stijlifer, Ploesoma Hudson!, Rattulus, Triarthra, Pedalion. If we remember 

 that the life of these organisms most probably can be counted only in hours, this 

 is quite intelligible. 



The knowledge we have now gained with regard to the excretory organs in 

 the males gives rise to the following remarks. There might be reason to suppose, 

 that there could, in the male sex, be pointed out some connection between the oc- 

 currence of the alimentary canal and the developmental stage of the excretory or- 

 gan; especially those who suppose that the water must come in through the ali- 

 mentary canal, and the contractile bladder therefore in some way be filled from 

 this organ, might expect that the contractile bladder would disappear where the 

 alimentary canal is lacking, rudimentary, or functionless. That this is in some 

 way really the case cannot be wholly denied; as mentioned above, it is a common 

 rule that all males without alimentary canal are destitute of the contractile vesicle. 

 On the other hand it must be remembered, that neither Rousselet nor I have been 

 able to find this last named organ in Rhinops vitrea, one of the very few males which 

 possess a fully developed alimentary canal and where therefore a bladder might be 

 expected. Further, that the Asplanchna males which are entirely destitute of any 

 alimentary canal, really possess a bladder, which is just as large as that of the 

 female and functions perfectly. With regard to all those authors who suppose that 

 the water currents in some way pass through the walls of the alimentary canal, it 

 must now be emphasized that the contractile vesicle in the males of the Asplanchna 

 is distended and emptied in quite the same manner as in the female sex, and this 

 in spite of the total absence of an alimentary canal. As far as 1 can make out from 

 our present standpoint of knowledge no other explanation is possible than that the 

 water most pass into the body cavity from the whole surface of the animal. The 

 driving forces are of course not the vibratile tags but only the difference between 

 the density of the two fluids inside and outside the body wall. It is the main task 

 of the vibratile tags to drive the water currents out of the body again. In the fe- 

 male sex they are provisionally stored up in the contractile vesicle from which they 

 are at regular intervals forced out of the body, in the male sex this is not as a rule 

 the case, and the water currents flow out uninterruptedly through the two openings 

 at the side of the genital opening. This view is only of value as a working theory, 

 but it might be tested by experimental investigation. If it is correct, our apprehension 

 of the whole organ as only excretory must be somewhat altered; its main task being 



