214 



ROTIFERA 



bladder, which also discharges at regular intervals into the cloaca 

 on its ventral or distal side (Figs. 106, U and 112). This bladder 

 may reach when expanded one-third the diameter of the whole 

 animal, and contract as often as three times per minute ; so that in 



Fig. 112. Apsilidae : A, Apsilus lentiformis, 9, dorsal view (after Metschnikoff) ; the 

 square brain is seen with nerves to the lateral antennae ; B, larva of A. lentiformis (?), 

 showing the paired eyes and ciliated cupped foot ; C, adult of Atrochus appendi- 

 cidatus, 6 (after Wierzejski). al, Lateral antennae ; am, median antenna (just in 

 front is seen the renal commissure) ; an, anus ; br, brain, below which the paired 

 eyes are seen ; c, cloaca ; em, embryo ; em', em", em'", three successive stages of 

 embryo.5 in the uterus of C ; k, kidney. The coarser muscles are striated. 



a period of nine minutes a bulk of water equal to that of the 

 animal must have diffused through the body-wall, to be removed 

 by the kidneys. It is obvious that while the function of the 

 kidneys is primitively excretory, the passage of the water through 

 the body must bring in the oxygen dissolved in the external 



