402 



SCIENCE 



[N. S. Vol. XLIX. No. 1269 



In conclusion, I suggest a simple rule for 

 obtaining the " score " as an approximation to 

 the "geometrical mean," namely Revert dilu- 

 tions' and apply Phelps Method.^ The process 

 of reversion gives the benefit of geometrically 

 reducing the data, and by applying Phelps' 

 Method one obtains an approximate " Geo- 

 metrical Mean." This is the principle success- 

 fully applied in " scoring " oysters. 



William Firth Wells 



Sanitary Corps U. S. A. 



CARDIUM CORBIS A MONCECIOUS BIVALVE 



In the work entitled " Tertiary Fauna of 

 Florida," Transactions of The Wagner Free 

 Institute of Science of Philadelphia, Vol. 3, 

 part 5, 1900, p. 1071, WiUiam H. Dall makes 

 the following observation with reference to 

 Cardia : " Nearly all Cardia have two forms, 

 one more equilateral and globose, the other 

 more oblique and elongated, but whether these 

 differences can be correlated with sex is at 

 present unknown." 



If attention has been called to the fact that 

 certain species of Cardia are moncecious, 

 since Dall made the above statement, the 

 writer of this note is not aware of it. 



Variation as mentioned in the above quota- 

 tion is very noticeable in the common Cardium 

 corhis Martyn of the northwest coast. On 

 preparing sections of the visceral region of 

 individuals of this species in recent studies, 

 their hermaphroditic character was clearly 

 shown, masses of ova being interspersed with 

 and sometimes completely surrounded by the 

 spermaries. 



I have not had the opportunity of ex- 

 amining other species of Cardia. They may 

 or may not be moncecious, but it is evident, 

 from the above observation on Cardium corhis 

 Martyn, that variations in this genus must be 

 based upon something other than sexual differ- 

 ences. C. H. Edmondson 



Zoology Laboratory, 

 University op Oregon 



' Standard Methods of Water Analyses, Report 

 Committee Am. Public Health Ass 'n, 1912. 



8 Phelps, Professor Earle B., Am. Jour. Puh. 

 Eyg., 18, 1908, p. 141. 



THE PASSENGER PIGEON 



To THE Editor of Science: In 1902, 1904 

 and 1905 I rented a house at Devon, about 

 sixteen miles west of Philadelphia, and on 

 several occasions a single passenger pigeon 

 visited my garden there. Doves came fre- 

 quently. I was near enough to the passenger 

 pigeon to make mistake impossible. Its color 

 and size would easily distinguish it from the 

 dove, as well as its method of flight and the 

 use of its tail in rising from the ground, 

 which is so much freer than that of the dove, 

 while the shape of its tail would make it im- 

 possible to mistake its spread tail for that of 

 a domestic pigeon. I was at Devon again 

 during the summers of 1907 to 1913 inclusive 

 and four or five times saw a single passenger 

 pigeon. The last time was while motoring in 

 1913. I was running swiftly along a road not 

 far from the woods and a bird got up by the 

 side of the road and after rising from the 

 ground about fifteen feet started off towards 

 the woods. When its flight changed from 

 semi-perpendicular to horizontal I was not 

 twenty yards from it and could clearly see its 

 breast and the under side of its tail and just 

 afterwards the upper side of its tail still 

 spread as the bird changed its course. I could 

 see where it got up on the road and had an 

 excellent idea of my distance, so that I could 

 judge of its size, as well as its color and the 

 shape of the tail. 



I have always felt very skeptical about the 

 " scientific " killing off of the last bird of a 

 species which was so broadly distributed and 

 most of whose haunts were so far from the 

 abode of any one who would be likely to write 

 for the papers. It may be what professional 

 scientists would call scientific, but to me, as a 

 business man, it has seemed pretty much like 

 jumping at conclusions and trading on one's 

 ignorance. F. R. Welsh 



QUOTATIONS 



THE BRITISH BIRTH RATE 



It is very difficult to bring home to people the 

 meaning of a tendency so long as that tend- 

 ency can only be expressed in figures. Yet 



