February 5, 1904.] 



SCIENCE. 



219 



It was shown that there is no good 

 evidence that lampreys feed except when 

 attached, and that, according to accepted 

 aeeountSj they breathe when free as when 

 attached, through the external branchio- 

 pores. There is thus apparently no occa- 

 sion for a backward current of water into 

 the mouth, either for the purposes of respi- 

 ration or for the purpose of feeding, and 

 the published observations and those of the 

 writer show that such a current is of rare 

 occurrence. It would thus appear that the 

 velar valves, water tube and valves of the 

 external branchiopore must serve chiefly 

 for the purpose of enabling a current of 

 water to be directed forward out of the 

 mouth. It was shown that such a current 

 is directed forward whenever the animal 

 cleanses the pharynx or mouth of irritating 

 foreign bodies and whenever it detaches 

 itself. Synchronously with the forwardly 

 directed current there is a closure of the 

 external branchiopore by means of the 

 ectal and ental valves described by Gage. 

 Hence water tube, velar valves and ectal 

 and ental valves of Gage find their ex- 

 planation chiefly in this forwardly directed 

 current. There was also described a pair 

 of jaws— the velar jaws, connected with the 

 velar valves. These jaws serve to hinder 

 the entrance of foreign bodies into the 

 water tube, and are so arranged as to close 

 when the water tube closes by the action of 

 the velar valves, and to open when the 

 water tube opens through the relaxation of 

 the velar valves. It was shown further 

 that the attached lamprey feeds not only 

 on the blood of its host (as stated by 

 Gage), but also on its soft tissues. 



*Some Reactions of Mneniioiosis leidyi: 

 George William Hunter, Jr., New 

 York City. (Read by title.) 

 Geoti'opism. — The animal becomes posi- 

 tively or negatively geotropic under condi- 

 tions seemingly intimately associated with 



the given supply of light and degree of 

 temperature. Stereotropisvi. — Mnemiopsis 

 exhibits marked stereotropism, especially 

 in the darkness. Large numbers of ani- 

 mals will frequently be found resting in 

 pockets in the eel-grass. They also exhibit 

 this same phenomenon in dishes in the labo- 

 ratory. Reactions to Light {Phototaxis 

 and Photopathy) . — Sudden light causes ac- 

 tivity; sudden darkness inhibits activity. 

 (This is partly in harmony with the find- 

 ings of Yerkes on Gonionemus. See 

 American Journal of Physiology, IX., 

 No. 5.) Orientation with reference to the 

 directive influence of the light rays (pho- 

 totaxis) was long sought for, but only ob- 

 tained in a few instances, with very strong 

 or focused sunlight. A large number of 

 experiments were made in dishes covered 

 with strips of red, blue and green glass. 

 It was found that in a given period of time 

 (one to ten hours, observations made every 

 half hour) the greater number of animals 

 were counted under the green glass. The 

 totals from 5 sets of experiments read as 

 follows: Blue, 90; red, 126; green, 235. 

 These results need much more careful 

 study before an explanation is ofiiered. 

 Effects of Changes in Temperature. — 

 Mnemio'^sis is relatively more resistant to 

 changes in temperature than is Gonionemus 

 (see Yerkes, American Journal of Phys- 

 iology, Vol. IX., No. 5). Responses to 

 electrical stimulation under condition of 

 decrease of heat show little change in reac- 

 tion time to 15° 0. ; lower than that a grad- 

 ual increase in reaction time until no reac- 

 tion is reached. Responses to electrical 

 stimulation under conditions of increase of 

 temperature show a slight quickening in 

 the reaction time up to about 29° C. After 

 that a rapid increase in reaction time. 

 Electrotaxis. — A definite orientation of the 

 animal is the immediate effect of stimula- 

 tion with a current of moderate strength 

 (one half to three volts, voltage taken in 



