430 NATURAL HISTORY AND ANATOMY OF 



tributed to them, and have a mottled appearance from nume- 

 rous microscopic organs attached to their external surface. 

 When a small portion of the respiratory organ is cut from the 

 living animal and placed under the microscope in a little sea- 

 water, the dots observed with the naked eye on its outer or 

 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 %v cavity, covered with cilia which 

 exhibit 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 The ciliated funnels could be withdrawn into the pouches 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 ex- 

 hibit 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 

 animal to fill the respiratory sacs by the following process. 

 By contracting the anterior part of its body, and pushing the 

 contained sea-water back, the animal distends its posterior 

 portion into a bulbous shape, in consequence of which the 



