374 Messrs Forbes and Goodsir on (he Natural History 



peritoneal surface, exhibit the appearance of a number of fun- 

 nels, with their necks attached, and their cup-like extremities 

 standing erect. Each of these funnels has its outer surface, 

 rim, and inner surface or cavity, covered with cilia which ex- 

 hibit lively motions. The inner or mucous surface of the 

 respiratory sac has a number of rounded somewhat lobulated 

 elevations on it, each corresponding to one of the funnels on 

 the outer surface. These elevations are covered with cilia, 

 but on the membrane between them none could be seen. 

 The ciliated funnels could be withdrawn into the pouches 

 formed by the ciliated elevations of the internal surface ; but 

 we could not obtain ocular demonstration of what we suspect 

 to be the case — that the cavities of the funnels open into the 

 common respiratory cavities, and that the ciliated elevations 

 of the inner surface disappear when the funnels in the outer 

 surface are extended ; and, vice versa, a current being in this 

 way established between the respiratory cavities and the com- 

 mon cavity of the body of the animal, which is full of sea- 

 water. The muscular fibres of the two respiratory sacs exhi- 

 bit a peculiar arrangement. Both the transverse and longi- 

 tudinal fibres have an undulating course so as to surround the 

 necks of each of the funnel-shaped organs as the fibres of the 

 human gravid uterus surround the uterine sinuses. If the 

 currents of sea- water flow through the funnels, the contraction 

 of the muscular fibres can stop that flow, and enable the ani- 

 mal to fill the respiratory sacs by the following process. By 

 contracting the anterior part of its body, and pushing the con- 

 tained sea-water back, the animal distends its posterior por- 

 tion into a bulbous shape, in consequence of which the en- 

 closed portions of the anal spines become widely separated ; 

 and from their connection with the cloaca, that cavity is di- 

 lated, and, acting like a syringe, sucks in more water. The 

 animal then closes the anus, and contracts the cloaca by push- 

 ing the water in its body forwards. This simultaneous action 

 forces the water contained in the cloaca into the respiratory 

 sacs, along which it is conveyed by their powerful vermicular 

 or peristaltic action. A slight relaxation of the muscular 

 fibres of the sacs, and the erection of the ciliated funnels, will 

 allow the water to pass into the cavity of the body, while the 



