CLOACAL PUMPING OF HOLOTHURIANS. 131 



leading to a graduated cylinder. Employing 10 individuals each 

 24-25 cms. in length, I found an average volume of 15.5 c.c. of 

 of seawater to be expelled in this way. 



If a cut through the body-wall be made rapidly around the body 

 of a Stichopus at the level of the anterior end of the cloacal cham- 

 ber (Crozier, '16), it is possible to obtain a preparation in which 

 the respiratory trees remain intact and preserve their normal con- 

 nection with the cloacal wall. Such a preparation will live for a 

 long time in seawater, and it can be seen that water is pumped, 

 as normally, into the respiratory trees, and that when these 

 organs have been expanded to a certain degree their contained 

 water is expelled in the usual manner. In this process the re- 

 spiratory trees themselves are actively contractile (cf. Iwanzoff, 

 '97; Henri, '03) ; they shrivel up almost, but not quite, completely 

 so that nearly all their contained water is expelled. The inde- 

 pendent nature of the activity of the cloaca and respiratory 

 trees affords a curious instance of the autonomy of the organs in 

 echinoderms. 



Examination of the interior of an intact Stichopus at the con- 

 clusion of " spouting " showed that the respiratory trees were in 

 this case also almost completely contracted. 



The cloacal chamber of Stichopus 24.5 cm. in length pulsates 

 with a frequency of 9.6 per minute (at 27), and 8 or 9 inspira- 

 tory pulsations intervene between two .expirations, each of the 

 latter occupying some 12 seconds (cf. Crozier, '16). On this 

 basis a Stichopus of this size will (at 27) take into its cloaca 

 about 15-5 c - c - f water during each 65 seconds, or about 859 c.c. 

 per hour; leading to an estimated amount of 20-21 liters per day, 

 assuming a uniform rate during the 24 hours. 



From the comparative standpoint, it must be remembered that 

 probably little or no food-getting is associated with the entrance 

 of water into the body of Stichopus by way of the cloaca, Put- 

 ter's ('07) notion to the contrary notwithstanding; but that, in 

 contrast to the situation in sponges and in ascidians, respiration 

 and excretion are in holothurians the sole functional implica- 

 tions of the water stream. In this way it can be understood that 

 the volume of water required by these animals is much less, even 

 in proportion to their size, than is the case with sponges, lamelli- 

 branchs, or ascidians. 



