No. 628] ONCHIDIUM AND ADAPTIVE COLOEATIOX .419 



where Onchidium abounds. A typical instance is tliat of 

 a low-lyin^ islet such as ''Little Agar 's," m (iimt Sdiiiid. 

 The leeward (eastern) side of this island, well inoLctcd 

 by the mass of llie larucr A-ar's Tshnul. > xpn., . .-it Unv 

 water a considerable extent of almost li..ri/<.iita^l rock- 



which are, lioweN ei'. mucli nioic ahniidant arouiid the ver- 

 tical edges of tlie^e ^Jabs. Within tlii' chnnj)s of Modio- 

 lus lie many Onchidium nests, from which the mollusks 

 at appropriate times creep out and wander over the flat, 

 yellowish, sunlit beach-rock. It is in situations of this 

 general type that OHcliidimn is most abundant; in less 

 freely illuminated places it occurs more sparingly. 



It is a remarkable fact that, in addition to fre(iuenting 

 characteristically, thonu'li not exclusively. h;d)itats which 

 during most of the dax' I'eceivc the (hi-ect i-;i\ s i»t llie 



hours^^and nex.T (in oni . x|-Mu,e, i .M lum.r. tL Tir- 

 cumstance which make, tlii^ (n,i,iiti..n iMitienl.tiK 

 curious is that 0. fJmid^nnnn al al' hm,^ ,nanlnJi/ 

 phofofropic, and in a \er\- pi'eci>e mannci'. when loted 

 apart from its usual env ironment. No more >tnki!m' in- 

 stance is km)wn to us ot apparent eonl rmin-t ion hdwccn 

 the findings ol an;il\ tieal e.\periniont;ilion rcunrdmu' the 

 behavior of an animal and the .-.etunl life of tho >ame 

 creature, toi the MiniU ^^\u n on the int itidal mrk^ moN(> 

 toward or awav fi'om the horizontal ravs of the sun with 

 ])erto,-t indiltei.-Pc.-. M'he eloudme.. o, hniiiitm ut the 



on the numl)ers ot ( )n('hi(ha which a])])ear u])on the rocks. 



