272 



THE POPULAR SCIENCE MONTHLY. 



sented by so great a name no sacrifice was 

 too great. 



We are nearly at the end of our space, 

 without, unfortunately, being nearly at the 

 end of our subject. The travels of Mr. You- 

 mans in England and on the continent of 

 Europe, sometimes in the company of Spen- 

 cer ; his correspondence with members of his 

 family in this country ; his labors in arrang- 

 ing for the publication of the International 

 Scientific Series, in connection with which he 

 visited Paris, Berlin, and Leipsic, and came 

 into personal relations with the leading sa- 

 vants of France and Germany ; finally, his es- 

 tablishment of The Popular Science Month- 

 ly, chiefly on the strength of a series of origi- 

 nal articles by Spencer, on The Study of 

 Sociology, would admit of extensive and in- 

 teresting treatment ; but foral! this we must 

 refer our readers to the book itself. The 

 aim of this notice has been to indicate to 

 the many who knew Prof. Youmans only by 

 name what manner of man he was, and what 

 services he rendered in the cause of intellec- 

 tual progress. Prof. Fiske, with the skill of 

 an accomplished writer and the sympathy of 

 an intimate friend and most sincere admirer, 

 has given the finer as well as the broader 

 lineaments of his character in a manner that 

 leaves little to be desired. That so energetic 

 a worker, with so capable a brain and so 

 large a heart, should have died at the com- 

 paratively early age of sixty-five is a matter 

 for profound regret, particularly as we are 

 compelled to attribute it to the same want of 

 care for his general health and over-devotion 

 to work which brought on, and then aggra- 

 vated, his early trouble with his eyes. As a 

 writer Prof. Youmans had a style of his own, 

 full of nervous force and grace a style 

 ample and rich, and yet admirably precise. 

 Some of his essays are published as an ap- 

 pendix to the biography, and form most in- 

 teresting and instructive reading. From these 

 his dominant ideas and purposes may be 

 gathered ; and no one can read many pages 

 without seeing and feeling that here was 

 no intellectual dilettante, but a man with 

 a mission, and that the lofty one of dissi- 

 pating ignorance and prejudice, spreading 

 the light of science, and preparing the 

 way for those "nobler modes of life" of 

 which seers have prophesied and poets 

 sung. 



THE GENUS SALPA. A Monograph, with 

 Fifty-seven Plates. By WILLIAM K. 

 BROOKS, Ph. D., LL. D. With a supple- 

 mentary Paper by MATNARD M. METCALF. 

 Memoirs from the Biological Laboratory 

 of the Johns Hopkins University. Vol. 

 II. Baltimore, 1893. Price, $7.50. 



THIS bulky quarto, with its companion 

 volume of fifty-seven plates, is a monu- 

 mental work. It is the result of years of 

 concentrated effort, and is a credit to Ameri- 

 can science. 



The subject of the investigation is a 

 pelagic or free-swimming Ascidian, confined 

 to the high seas, and exceptional even in a 

 group whose larvae are plainly allied to ver- 

 tebrates, while the adults have lost nearly 

 every resemblance to their vertebrate allies by 

 the degeneration and loss of their vertebrate 

 features. Salpa is aptly described by Prof. 

 Brooks as a transparent swimming Tunicate, 

 which in effect is "an enormous pharynx 

 which swims through the water, gulping in 

 great mouthf uls at each contraction fti its 

 muscles." Happily the supply of radiolarian 

 and diatom food is unlimited, and hence Sal- 

 pae multiply in immense profusion and with 

 astonishing rapidity. 



Salpse under favoring conditions of food, 

 and perhaps other physical causes not dis- 

 cussed by the author, reproduce both sex- 

 ually and asexually. Each species has two 

 generations in its life-cycle, known as the 

 solitary generation and the aggregated gen- 

 eration. Chamisso, the poet, novelist, and 

 biologist, first discovered this. The solitary 

 salpa is born from an egg which is carried 

 within the body of the aggregated salpa, 

 whose blood nourishes the embryo during 

 its development by means of a nutritive pla- 

 centa. On the other hand, the aggregated 

 or chain salpaa are produced asexually by 

 budding from the body of the solitary salpa. 



This placenta, as Brooks shows, contrary 

 to the views of some writers, has only a su- 

 perficial resemblance to the foetal organ of 

 the mammals ; it is an independent structure, 

 being in the salpa only of use in conveying 

 food to the embryo. This food has been 

 discovered by the author to be great placenta 

 cells which migrate from the body of the 

 chain salpa into the body cavity of the em- 

 bryo. Hence the embryo salpa stands in a 

 much more direct relation to the external 

 world than the mammalian embrvo. 



