636 



SCIENCE. 



[N. S. Vol. IV. No. 93. 



The rhythm used is that of a movement of 

 the forearm. A series of movements is made 

 in a natural rhythm, then other series in unnat- 

 ural rhythms. The average and the mean varia- 

 tion (mean error) ai-e computed for each series. 

 The psychological mean variation (all apparatus 

 errors being rendered negligible) is a good meas- 

 ure of the subject's irregularity or of the diffi- 

 culty of his mental processes. Using the mean 

 variation thus as a measure of the disadvantage 

 of a rhythm, we can express the relation of dis- 

 advantage to length as m ^/ (r) where m is the 

 mean variation and r the length of the rhythm. 

 Now, the law that I believe myself able to as- 

 sert is 



= const. 



abs (r — B) 



where m and r have the same meanings as be- 

 fore, B is the length of the natural rhythm and 

 abs indicates that the sign of the quantity is 

 disregarded. In other words, the amount of 

 irregularity is proportional to the amount of 

 deviation from the natural rhythm. 



The full proof of the law with a determination 

 of the constants I hope to furnish during the 

 coming year. E. W. Scripture. 



Yale University, September 20, 1896. 



SCIENTIFIC LITERATURE. 

 The American Lobster : A Study of Its Habits and 

 Development. By Francis Hobart Her- 



RICK. 



This monograph, issued as a portion of the 

 Bulletin of the U. S. Fish Commission for 1895, 

 has over 250 pages of text and 64 plates, and 

 represents the work of the author as an investi- 

 gator of the U. S. Fish Commission from 1890 

 to 1895. Its general appearance is quite up to 

 the improved standard of the more recent gov- 

 ernment publications. The typography is good 

 and many of the plates are really excellent. 



It is presumed that the publications of the 

 Fish Commission will have some practical bear- 

 ing upon the innumerable problems of fish-cul- 

 ture, and Dr. Herrick has not confined him- 

 self to mere questions of morphology and 

 embryology, but, following the suggestion of 

 Prof. Eathbun, has endeavored to determine 

 the natural history of this most important and 



strangely persecuted invertebrate ; and it is to 

 be hoped that with these natural data at hand 

 the government will adopt some rational method 

 of experimentation which shall finally lead to 

 successful lobster culture. 



In the Introduction the author considers the 

 immediate questions of nomenclature, the meth- 

 ods of lobster capture, and the rise and inexcu- 

 sable decline of the lobster fishery in America. 



Chapter II. deals at considerable length with 

 the general subject of reproduction. The essen- 

 tial and secondary organs are described, the 

 peculiar pairing habits of certain Crustacea are 

 mentioned, and the methods of oviposition are 

 discussed. In describing the spermatozoa the 

 author writes : ' ' The sperm cells have a char- 

 acteristic shape and are absolutely immobile in 

 the conditions under which they are ordinarily 

 observed, but it is impossible to suppose that 

 this is always the case." The reviewer has 

 seen the spermatozoa in active movement, 

 swimming across the field of the microscope 

 with the same nervous contractions that are 

 characteristic of the Hydromedusse. 



The facts collected in reference to the time 

 of egg-laying and period of incubation are very 

 complete, and indicate the time when artificial 

 hatching should commence. We cannot, how- 

 ever, agree with the author that there are at pres- 

 ent adequate data for the assumption that eggs 

 are frequently deposited during the fall and 

 winter. When the temperature of the water is 

 known to be so important a factor in the rate 

 of development, and when the range of tem- 

 perature variation is from 35.5° F. in February 

 to 71.4° F. in August, it is extremely hazardous 

 to estimate the actual age of ' winter ' embryos 

 from the known age of those whose growth 

 has been accelerated by the warmer water of 

 midsummer. 



The data illustrating the law of production, 

 arranged in Table XV., have been gathered 

 from an examination of 4,000 adult lobsters, 

 and represent a vast amount of work. The re- 

 arrangement of this material in other tables, 

 and the author's conclusions regarding the 

 period of greatest fertility, are especially in- 

 structive. 



In dealing with the destruction of the egg- 

 lobster and its spawn, it is to be regretted that 



