March 27, 1908] 



SCIENCE 



489 



from Beaufort, N. C, opening ventro- 

 laterally upon the surface of the cerebral 

 organ and running backward into the sub- 

 stance of the brain. The photic organs of 

 Sipmuiid'us, which hitherto have not been 

 positively recognized, resemble those of 

 Phymosoma, as described by Shipley; 

 those of Phascolosoma verrillii diifer from 

 them in being relatively much larger and 

 more highly developed, having in the 

 middle of the ocular tube a spindle-shaped 

 lens. The walls of the posterior part of 

 each ocular tube are composed of long 

 conical pigmented cells, of which the bases 

 abut against the tube, the apices radiate 

 into the surrounding tissues of the brain. 

 Neurones with cylindrical distal ends, 

 covered with longitudinal fibrillse, lie in a 

 group behind and below the posterior end 

 of each ocular tube. They are probably 

 adapted to receive photic stimuli, the im- 

 pulse being transmitted from them, mainly 

 over bipolar neurones, directly to the 

 retractor muscles. The reaction time of 

 these muscles to photic stimuli, in P. vul- 

 gare at least, is notably less than that of 

 the longitudinal muscles of the body wall. 



Parallel Development in Trematodes : H. 



S. Pratt, Haverford College. 



When a genus of trematodes is widely 

 distributed over the earth it is probable 

 that the species constituting it are not 

 necessarily closely allied, but have, in cer- 

 tain cases at least, acquired a similar struc- 

 ture because they have been subjected to 

 similar conditions of life through long 

 periods of time. Thus the four species of 

 the genus Fasciola inhabit the gall-passages 

 of large herbivorous mammals in the four 

 largest continents, and the ten species of 

 the genus Pneimionosces living in the lungs 

 of frogs and toads are almost as widely dis- 

 tributed. It is hard to see how the species 

 in each of these genera, as well as in others 

 that might be mentioned, could be de- 



scended from a common ancestor and have 

 migrated from a common center to the 

 localities where they are at present found, 

 since the conditions of existence of a tre- 

 matode, bearing as it does a fixed and 

 very definite relation to two hosts, make 

 migration a difficult matter for it. On the 

 other hand, trematodes living in the livers 

 of large herbivores or in the lungs of frogs 

 and toads, even in very different parts of 

 the world, have been subjected to identical 

 and constant environmental conditions 

 while passing thiough their phyletic de- 

 velopmental stages, with the result that 

 they are now so similar in structure that 

 they are classified in each of these cases in 

 the same genus. 



The Distribution of the Amphipods occur- 

 ring in Bermuda: B. W. Kunkel, Tale 

 University. 



The most interesting fact regarding the 

 occurrence of the littoral amphipods of 

 Bermuda is the large number of species 

 which are also found in the Mediterranean. 

 'Of the 45 species, representative of 27 

 genera, which have been found in Ber- 

 mudian waters, besides one species of 

 Cyamus reported by Verrill from a whale 

 landed at St. Georges, nearly one half 

 (20-21) are common Mediterranean forms. 

 Only four Bermuda species, which are not 

 endemic, are wanting in the Mediter- 

 ranean. Twenty species are apparently 

 peculiar to Bermuda. 



The amphipods of the West Indies and 

 Central America, with which the Bermuda 

 forms probably are most closely related, 

 have not been at all carefully studied, so 

 that at the present time it is impossible to 

 draw any conclusions regarding the exact 

 relationship of the two faunae. 



Next to the Mediterranean, the region 

 which presents the greatest number of spe- 

 cies in common with Bermuda is Great 

 Britain with 14 species; then follows the 



