440 J. H. ORTON. 



dredgers find very troublesome, namely, the curious habit of sticking 

 together in long chains by one individual sitting on the back of 

 another. These chains are without doubt permanent collections of 

 individuals, as can be seen from the following facts : — 



(1) The accurate fitting of the edge of the shell of each animal into 

 the crevices and irregularities of the surface or shell upon which it is 

 seated ; hence, only short periods of separation could be possible. 

 Thus the animal has, so to speak, grown in the position. 



(2) In cases where a chain is attached to soft rock, the proximal 

 individuals wear in the rock itself a deep impression of the edge of the 

 shell by a lateral movement, probably executed in the search for food. 

 In this way the animal becomes seated on a boss of the rock with a pit 

 all around it. 



(3) Experiments on separating the members of chains, and giving 

 the animals an opportunity of re-chaining, indicate that the older 

 animals can only re-attach themselves to anything with difficulty, but 

 attach themselves most easily to a smooth surface. If a number of 

 such animals be left in a dish, they make no attempt to re-chain in 

 their previous order, and indeed large specimens appear unable to move 

 about, or move only with great difficulty. 



By supporting dismembered individuals of a chain in the same 

 relative positions which they occupied before being separated, I have 

 succeeded in re-forming a number of chains, but in order to effect this 

 it is necessary to place the animals close together, and to keep a close 

 watch on them, so as to replace them should they fall out of position. 

 In many cases, however, even with such care, the animals are apparently 

 unable to re-attach themselves. 



(4) Prof. Conklin states that old individuals sometimes become per- 

 manently fixed by a calcareous secretion of the foot, and recently I 

 have observed several old individuals which appeared to be just 

 beginning to form such a calcareous attachment. 



(5) I have kept a number of chains of Crepidula alive for as long a 

 -period as a year without the members of a chain separating, except in one 

 or two cases, which may thus be regarded without doubt as exceptional. 



Thus there would appear to be no doubt that the chains are per- 

 manent. The chains, however, are composed of almost entirely 

 middle-aged or elderly Crepidulas, so to speak. But the very young 

 ones are motile, and move about from place to place. I have shown 

 elsewhere that Crepidula is a protandric hermaphrodite, that is to say, 

 that all the individuals are born as males, and, passing through an 

 apparently hermaphrodite stage, change into females. Consequently, 

 chains are formed in the following manner : — 



