448 On the Phcmomena of the Reproduction of the Chitons. 



stage of development showed no metamorphosis that I could 

 perceive. 



On the 26th July the animal was evidently more detached 

 from its cell, as the five anterior valves were distinctly marked 

 and the fringe margin was detected ; the three posterior valves 

 were still covered by the enveloping skin, but traceable through 

 the diaphaneity of the membrane. The animal still swam with 

 unabated vigour. On the 29th and 30th it had altogether cast 

 off the embryonic covering and exhibited the complete form of 

 the Chiton. During these phases of development every point 

 posteally and anteally appeared destitute of accessories, except 

 the usual circumferential fringe ; no antennae, tentacula, eyes, 

 caudal appendage, articulated feet, bristles or filaments were 

 discoverable, nor any other exserted organ. At this period 

 nearly all natatory motion had ceased, the animal remained 

 apparently fixed at the bottom of the saucer, and only a slight 

 change of place was perceptible with a good lens. 



The animal in its phase of rapid movement often rolled itself 

 into a ball, which led me to think there might be some alliance 

 between it and the crustaceous Articulata, particularly with the 

 Oniscus entomon, as I have often seen adult Chitons involve 

 themselves in a somewhat similar globular form. Notwith- 

 standing these traits of relationship with other tribes, it cannot 

 admit of doubt, from M. Cuvier^s dissections and our own de- 

 tailed account of the animal, that the Chitons are far nearer to 

 the Mollusca than to any other class ; for though we may observe 

 some traces of approach to certain sections of the Crustacea in 

 the segmental disposition of the hard parts, still this condition 

 does not obtain in the soft parts of the body, which are inarti- 

 culate or molluscan ; and we may add that the testaceous pieces 

 are not connected by articulation, but merely overlap each other. 

 The supposed relation to other divisions, the annelidan and cir- 

 ripodan Articulata, is still slighter, and does not with the former, 

 as to external organs, extend much beyond the marginal fringe, 

 which may have an equivocal assimilation with the feet, bristles 

 and tufts of hair of that vermiform tribe ; and with the latter 

 there is some community by the somewhat similar division of 

 the cone into distinct pieces. 



These quasi alliances may perhaps induce us to admit that 

 the Chitons may be the immediate precursors or the stage of 

 transition from the Articulata to the Mollusca, which of course 

 takes precedence of all the divisions of the Articulata ; that is, 

 the order of natural position in the ascending scale should be : 

 Annelida, Crustacea, Insecta, Mollusca. 



It is difficult to account for or explain the propelling power 

 of the rapid natation of the Chitons ; it may probably be due to 



