April 4, 1902.] 



SCIENCE. 



531 



equally distributed to the later cells. In a 

 less degree, the same thiug occurs in the 

 pollen cells of such plants as the geranium. 

 No fusion of the chromosomes is necessi- 

 tated in the slip ; hence, they continue to 

 lie side by side and divide in the ordinary 

 way, and the neAv plant is practically a 

 continuation of the old one. 



Relative Variability of Pectens from the 

 East and West Coasts of the United 

 States: C. B. Davenport. 

 Pecten irradians from Tampa, Florida, 

 and Pecten ventricosus from San Diego, 

 California, are closely related species, as 

 the parallelism in color and markings indi- 

 cates. They are a pair of species that, 

 taken by themselves, favor the view of a 

 recent connection of the Gulf of Mexico 

 and the Pacific Ocean. In respect to the 

 symmetry of the valve and in respect to 

 the globosity (height divided by length), 

 the San Diego form is much the more vari- 

 able, as measurements and calculations of 

 "the index of variability of ten hundred 

 shells prove. This greater variability of 

 the Pacific form is a fact in agreement with 

 what Eigenmann has found for fishes. It 

 is correlated with the greater physiographic 

 changes in recent times in the character of 

 the shore line of southern California as 

 contrasted with Florida. 



An Experimental Study of the Develop- 

 ment of the Lateral Line in the Frog 

 Embryo: R. G. Harrison. 



The Ovary and the Eeprodvctive Period: 



F. H. Herrick. 



"Whenever it is impossible or impracti- 

 cable to determine the reproductive periods 

 of an animal by watching its behavior, 

 - the structure of the ovary will usually fur- 

 nish the clue. This is true of the Crusta- 

 cea, and probably of all other animals. 



My present object is not only to illustrate 

 this fact, but also to settle definitely the 



spawning habits of the American lobster, 

 concerning which doubt and disagreement 

 still abound. To put the specific question 

 briefly: How often does an adult female 

 lobster lay her eggs i. The answer is, every 

 two years, as a rule. This same conclusion 

 was reached six years ago, chiefly from a 

 study of the comparative anatomy of the 

 ovary of animals captured at different sea- 

 sons, and while confident of its general ac- 

 curacy at that time, it is now possible to 

 supplement it with observations upon the 

 living animals themselves. 



In a single generation of ovarian eggs 

 three stages may be conveniently chosen 

 for special study: (1) The initial stage, 

 when the ova of the preceding generation 

 are laid; (2) the intermediate stage, when 

 those eggs are hatched; and (3) the final 

 stage, when the ovarian eggs have reached 

 their full size and are ready to be expelled 

 from the body. The average size attained 

 by the ova at these successive periods can 

 be determined with sufficient accuracy. 

 The time interval between stages 1 and 2 

 is known to be approximately one year. 

 The ratio of growth between stages 1 and 

 2 is approximately equal to the ratio of the 

 volume of the laid egg and that of ova in 

 the second stage, from Avhich it follows that 

 the time interval between stages 2 and 3 is 

 also one year. Further anatomical facts 

 and experiments with living animals also 

 confirm this conclusion. 



The adult spawning lobster therefore 

 does not lay her eggs each year, as some 

 have maintained, but every other year, al- 

 though this normal biennial period is likely 

 to be shortened or lengthened in individual 

 cases. The evidence on which these conclu- 

 sions rest is ample, and will be given in 

 detail at a later time. 



M. M. Metcalf, 



Secretary. 

 [To ie continued.'i //V 



