NOTES ON SOME PROBLEMS OF ADAPTATION: 5. THE 

 PHOTOTROPISM OF LIMA. 1 



W. J. CROZIER, 

 ZOOLOGICAL LABORATORY, RUTGERS COLLEGE. 



The monomyarian lamellibranch Lima is said (Kafka, '14, p. 

 393) to be "photoptic," i.e., reactive to light but not to shadows. 

 The statement may be applied to the species of Lima found in 

 some abundance at Bermuda, but there are certain additional 

 features about the photic responses of this animal which merit 

 a more extended notice. 



Polimanti ('12) has distinguished three types of locomotion in 

 Lima hians: (i) by the use of the foot as a lever; (2) by closure 

 of the valves and retraction of the tentacles (Butler, '91) ; (3) by 

 the expelling of water through the siphons. The first of these 

 types may however have some complex aspects. 



Lima was usually obtained near low water, around the edges 

 of large stones, and among smaller stones piled together loosely, 

 in bays where a certain amount of silt was being deposited; but 

 was also encountered on the reefs, in crannies between corals, 

 and sometimes among colonies of Ecteinascidia. It is decidedly 

 photonegative in its behavior, although this activity may be 

 lost after some days of laboratory captivity in open dishes. 

 The edge of the mantle is beset with long tentacles, which are 

 only very slightly adhesive toward wood or glass, but upon which 

 carmine particles stick and accumulate readily. When touched, 

 these tentacles react individually, by a vigorous and complicated 

 retraction, but the reaction time is curiously long (about I 

 minute, after a vigorous prod). They are reactive also to strong 

 currents of sea water, and respond vigorously to the local applica- 

 tion of a gentle stream of fresh water. At rest, the long white 

 tentacles are widely extended (for a good figure, cf. Nutting, '19, 

 p. 93). The tentacles are quite sensitive to weakly acid solu- 

 tions; and, after the animal has been for a time in darkness, 



1 Contributions from the Bermuda Biological Station for Research, No. 131. 



102 



