72 CHAS. W. HARGITT. 



been said that during this time the specimens remained rather 

 continuously within the tubes. Did they depend wholly upon 

 a reserve food supply? 



It may not be possible to answer these queries fully, but of 

 the correlation of the skin in the function of respiration there 

 can be no serious doubt. In my earlier experiments on Hydroides 

 ('06) it was found that when the gills w r ere excised to test their 

 relations to sensory reactions the creature did not seem to suffer 

 any serious inconvenience as to respiration. So in the case of 

 Protida, there was no evidence to the effect that respiration w r as 

 not normal during the long period of gilless life. Bounhiol 

 (1900) has reached similar conclusions from experiments on 

 Spirographis. He finds that respiration takes place through 

 both skin and gills, and that they supplement each other by 

 compensatory interaction. He finds also that it is apparently 

 easier for the gills to assume extra work than for the skin, and 

 that in excretion of COz the skin normally excretes about three 

 fourths of the entire amount. 



In the third place, there is the interesting query as to the 

 sensory function. I have shown that for Hydroides light per- 

 ception is almost exclusively a function of the gills. In Protiila 

 this is not so certain. Its behavior in this respect is less easily 

 controlled, owing to the sulking disposition of the worm. But 

 it is quite certain that autotomy did not result in entire inhibi- 

 tion of reaction to shadows and it may not be improbable that 

 something of sensory compensation may obtain in this, as in the 

 respiratory activity; or possibly this sensory function may be 

 shared in part with sonic other head-organ, possibly the mantle 

 margin, which in normal lite is often extended over the orifice of 

 i he tube, hence in a position admirably adapted to such a function. 



Concerning the entire matter of the significance of autotomy 

 little can be said. Such phenomena, similar in many respect^, 

 are well known among other animal groups, though not common 

 in any case, unless we may include phenomena of fission which 

 is a very familiar feature in many annelids; but this MVDIS to be 

 a wholly different problem. That it is spontaneous, hence not 

 attributable to the operation of gravity, contact, etc., seems 

 very evident. 



