INTESTINAL RESPIRATION IN ANNELIDS. 795 



Aphroditid^. 

 Aphrodite aculeata. 



Three specimens, which had been in captivity for a week, were used for the following 

 series of observations and experiments. They were examined in an oblong glass dish 

 containing a quantity of sand, in which they half buried themselves. 



The hinder end of the animals is, when they are quiescent, turned up, or even some- 

 what recurved over the body ; the margins of the flat and sole-like ventral surface are 

 approximated to each other some little distance from the (morphological) posterior end 

 of the animal, so that the appearance of a spindle-shaped aperture is produced, whose 

 sides are formed by the hindmost portions of the margins of the ventral surface with 

 the neighbouring setse. Owing to the hinder end of the animal being bent upwards as 

 above described, this apparent aperture faces upwards and backwards, and its actual 

 upper or anterior end is the morphological posterior end of the body. The appearance 

 is characteristic, but I cannot find that it has any functional importance, and I have 

 described it only because the spindle-shaped gap might, on a cursory examination, be 

 mistaken for the anus. The anus is, when closed, an inconspicuous crescentic slit, 

 concave backwards, on the dorsal surface just in front of the posterior end of 

 the animal. 



If, now, one of these animals be closely watched, the following succession of events 

 will probably be found to occur. From time to time the approximated margins of the 

 posterior portion of the ventral surface, which together have the spindle-shaped outline 

 described above, diverge ; the hinder end of the animal is in some degree depressed, as 

 when a dog with an erect tail puts it down ; the anus opens, and appears for about the 

 length of two seconds as a conspicuous circular aperture, now looking upwards ; the 

 anus then closes again, the tail is erected, and the posterior end of the ventral surface 

 resumes the appearance of a spindle-shaped slit. 



During the time when the arius is open, a jet of water is being expelled. This may 

 be shown in several ways. Thus if the surface of the water in the dish be carefully 

 watched, it will show a fountain- or jet-like elevation immediately above the anus at 

 the moment when the anus is open. Behind one of the specimens, in which the 

 posterior end was quite flat and not erected, and in which therefore the anus when open 

 faced backwards, a little heap of sand was placed during the interval between two ex- 

 pulsions ; this heap was blown away by the next jet expelled from the anus. Or 

 carmine particles suspended m the water may be used to demonstrate the current. 

 Both the quantity of water expelled and the force with which it escapes are obviously 

 considerable : even when the animal is in water of some depth, a jet is raised on the 

 surface at the moment of expulsion. 



The hinder end of the animal is not always erected ; when the animal is crawling 

 about it may be quite flat. The object of erection is probably to keep the anus above 



