474 



J. H. ORTON. 



to the smallest at the top.* Each individual does not sit in the middle 

 of the back of the one immediately below, but with the right anterior 

 edge of the shell touching the same part of the shell next below. As 

 a result each animal topples over a little to the right of the one below 

 it, so that the chains really form spirals (see Fig. 19). This arrange- 

 ment has some relation to the mode of feeding, for by the toppling 

 over to the right each individual is given a maximum area of water to 

 draw on from the left side for its food-current, which it will be remem- 

 bered is drawn in at the left. Moreover, the approximation of the 

 right sides of all the individuals of a chain results in a combination of 

 the exhalent currents, which must give excellent results in removing 

 effete products from the chain. The combined exhalent currents will 

 doubtless also assist the smaller individuals in the chain by reducing 

 the pressure of the water in the region of the exhalent aperture, and 

 thus enabling them to pass a greater volume of food-bearing water 

 through their mantle cavities than they otherwise could. 



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Fig. 19. — Postero-lateral view of a chain of seven individuals of Crepidula to show the 

 separate ingoing and the combined outgoing current of all the individuals in the 

 chain. (Natural size.) 



These advantages of chain formation are to be added to those already 

 noted (2, p. 479), and it may be remarked that the copulation of tlie 

 smaller with the larger individuals there suggested as probable has now 

 been observed a good many times, and contrary to what Prof. Conklin 

 has suggested (1, p. 16), several times by the same individuals, and by 

 individuals separated from each other by one or two of their fellows. 

 These observations, however, are still being carried on. 



* See (2) pp. 469-80 for a fuller description of chain phenomena. 



