90 



SCIENCE. 



[N. S. Vol. XXII. No. 551. 



of the same size and appearance were observed 

 in the culture, but none were seen behaving 

 in an abnormal way. As I did not realize 

 that I had been witnessing anything unusual 

 until the final catastrophe, the time occupied 

 by the division and the subsequent events up 

 to the disruption of the short-lived half was 

 not noted. The whole operation lasted but a 

 short time, probably little longer than one 

 minute. Edwin Linton. 



HOMING OF FISSURELLA AND SIPHON ARIA, 



The Patella is the only mollusc whose hom- 

 ing powers have been investigated. Fissurella, 

 a rhipidoglossate prosobranch, and Siphonaria, 

 which stands on the border line between the 

 opisthobranchs and the pulmonates, while dif- 

 fering more or less widely from Patella in 

 structure, closely resembles it in the form of 

 the shell and in their littoral habits. It was, 

 therefore, an interesting question whether 

 they resemble it also in the possession of the 

 homing power, A stay at the Bermuda bio- 

 logical station in the summer of 1903 gave 

 an opportunity to answer this question, al- 

 though a few days only being available for 

 the investigation, it was by no means as comr 

 plete as could be wished. Such as it is, how- 

 ever, I present it for the benefit of future 

 students of the subject. 



The specimens studied were Siphonaria 

 alternata Say and Fissurella harhadensis 

 Gmelin,^ Both are abundant at Bermuda, 

 where they live clinging to the exposed faces 

 of the bare rocks between tide marks. Bare 

 rocks, I say, for to a New England eye one 

 of the most striking features of the Bermuda 

 coast is the entire absence of the larger algse, 

 which upon our own rocky shores shelter so 

 large and varied a fauna. The rocks are 

 calcareous, soft and of irregular surface and 

 the home of Siphonaria is recognizable by a 

 greenish spot where the foot has rested. That 

 of Fissurella, as my notes show, is also clearly 

 marked, though I have carelessly omitted to 

 note how it may be known. Both species, as 

 will be seen from the following notes, exhibit 

 undoubted though limited homing powers. 



^ These specimens were kindly identified for me 

 by Mr. Charles ^W. Johnson of Boston. 



In marking animals and scars Higgins's 

 water-proof ink was used. White paint, which 

 was used by Davis, was not accessible, but as 

 the ink marks last about three days they are 

 fairly satisfactory. Siphonaria, being com- 

 paratively small, was readily removed from its 

 scar; Fissurella I was seldom able to detach 

 uninjured, and, accordingly, my observations 

 upon this species were limited almost entirely 

 to watching its voluntary departures and re- 

 turns. As might be anticipated, the animals, 

 unlike Patella, remain motionless on their 

 scars during low tide, moving, if at all, only 

 when the incoming water has moistened and 

 cooled their immediate surroundings. 



Siphonaria^ did not home when removed to 

 a distance of more than six inches and were 

 most likely to return when removed not more 

 than two inches, A quiet and shallow tide- 

 pool furnished the most favorable conditions 

 for their return. If the animal, on being 

 transferred, was set down with its head away 

 from the scar, it turned in the proper direc- 

 tion and, so far as I could judge, those headed 

 away were quite as likely to get back as those 

 headed toward the scars. In general, animals 

 which lost their way seemed to crawl restlessly 

 about for two or three days; each time one 

 was visited it was found in a new place. One, 

 however, settled down at once in a new home 

 and at the end of the third day had made a 

 discolored spot. On being transferred to his 

 old home he apparently failed to recognize it 

 and immediately crawled away. Usually the 

 scar was recognized at once by a returning 

 wanderer, and on reaching its edge he would 

 turn about, if necessary, so that his shell might 

 fit the scar, would slip on to it and settle 

 down, Siphonaria alternata thus appears to 

 have a sense of direction, the ability to recog- 

 nize its own recently-left scar, and the power 

 of homing when removed not more than six 

 inches. 



Experiments with Fissurella, as I have said, 

 were usually unsuccessful. That these mol- 

 luscs have the power of homing is seen, how- 

 ever, by watching them. As soon as the tide 

 has so covered him that he is not exposed to 

 the wash of the waves a Fissurella is very 



