PEDAL LACERATION IN ACTINIANS. 83 



after its separation from the parent individual. The acontia, 

 which in laceration pieces of this form are at first so prominent, 

 are later either withdrawn inside the cavity of the fragment, or 

 else they are broken off before the open side of the piece has closed 

 to any considerable extent. 



Immediately after the separation of the fragment there takes 

 place a rolling-in of the free edges, due principally to the elasticity 

 of the mesoglea, so that for some little distance within the cavity 

 is lined with ectoderm (Fig. 7. PI. II.). For some hours after 

 the separation of the fragment there is no visible external change 

 other than an increasing loss of color about the orifice of the tear 

 where the laceration piece was separated from the parent indi- 

 vidual. 



The next noticeable change appears as a turning upward of that 

 portion of the fragment in which is situated the original opening, 

 which by this time has become markedly reduced in extent; al- 

 though, contrary to the results of Hazen (1902), who worked with 

 fragments obtained by cutting off pieces including portions of the 

 column wall and pedal disc from adult specimens of Sagartia 

 IUCCB, in none of my specimens did the opening become entirely 

 obliterated. The new growth which brings about this change 

 in the shape of a laceration piece is much the more rapid on the 

 lower-pedal disc-side of the aperture. So that for some time the 

 elevated area is situated near the former internal edge of the 

 fragment. The wall that has come from the up-growth from 

 the pedal disc is nearly perpendicular, while the opposite side of 

 the fragment slopes away much as in its former manner (Fig. 2, 

 PI. I.). 



In a stage of development such as is represented in Fig. 2 

 there has already appeared the beginning of the tentacle buds, 

 and internally, of course, the earliest mesenteries. 



In a later stage, as in Fig. 3, PI. I., the readjustment of mate- 

 rials had proceeded farther in what is practically the same course. 

 The fragment as a whole has become much higher. The oral 

 end has nearly the same diameter, while farther down toward 

 the pedal disc the diameter is relatively much decreased. At 

 the base, however, the fragment still covers practically the same 

 area as when it was torn off from the parent animal. When 



