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LESLIE B. AREY AND W. J. CROZIER 



Figure 8 illustrates this point. When a chiton, partially out of 

 water, on the wall of an aquarium, swings from a vertical posi- 

 tion (fig. 7) to one such as that shown in figure 8, the posterior, 

 elevated part of the girdle travels to one side as a smooth wave. 

 The water current also enables a chiton to sample the surround- 

 ing water. It is of importance for reproduction, since the stim- 

 ulus to egg laying is provided by the diffusion of sperm from 

 near-by males; these sperms are carried past the openings of the 

 oviducts, past the 'osphradia' (p. 253), and eggs are liberated 



/ 7 8 



Fig. 7 Illustrating the course of the water current n Chiton. Diagram- 

 matic. 



Fig. 8 The course of the water current in Chiton when the animal is par- 

 tialiy submerged. Diagrammatic. 



in their company (Metcalf, '92; Heath, '99, '05 c). The ne- 

 phridia also discharge their excretions into the respiratory cur- 

 rent. These excretions, together with the water that has been 

 'used,' are usually shot to a considerable distance, because, the 

 anal opening being smaller than the incurrent openings, the 

 velocity of the outgoing current is high; here also, as in Ascidia 

 (Hecht, '18), the 'used' water is discharged in such a way that 

 it is not readily employed again for breathing purposes. 



The ventral surface of the girdle is transversely ribbed, pro- 

 viding minute channels through which water is taken in, even 



