SKETCH OF WILLIAM KEITH BROOKS. 405 



the Ascidians were broiiglit into line as ancestral vertebrates, it was 

 no wonder to find Professor Brooks laboring upon these interest- 

 ing creatures, but his work in this group started from a different 

 point of view. As early as 1875, when studying in the laboratory 

 of Alexander Agassiz, he contributed to the Boston Society of Natu- 

 ral History a description involving a most novel interpretation of the 

 embryology of a remarkable Ascidian, Salpa. This form is known 

 to many not naturalists as that beautiful animal chain which is some- 

 times so common in the clear waters of ISTewport Harbor as to be 

 dipped up in every bucket of water, but more often not there at all. 

 The female buds forth male branches and gives each an egg (which 

 is fertilized to form a second generation of females). There is thus 

 no alteration of sexual and non-sexual generations at all ; and, with 

 characteristic appreciation of a paradox, Professor Brooks subse- 

 quently emphasized the fact that the poet naturalist Chamisso, in 

 discovering, in 1814, " Alternation of Generations " in Salpa, had 

 discovered a phenomenon where it did not exist, though subse- 

 quently found common enough in many other animals. With the 

 continuity of interest so marked in him, the life history of Salpa, 

 as thus revealed, continued to be one of the living thoughts in Pro- 

 fessor Brooks's mind for a long period of years, and, with the accu- 

 mulation of material and results of researches afforded by his sum- 

 mer work, culminated in the monograph Salpa — a quarto of nearly 

 four hundred pages and fifty odd plates — published in 1893, or after 

 nearly twenty years of sustained interest in this complex problem. 

 In this volume we find first a coherent view of the intricate life 

 history of this animal illuminated by such metaphors as make the 

 necessary technicalities both readable and thinkable. For instance, 

 " A chain of Salpa may be compared to two chains of cars on two 

 parallel tracks, placed so that the middle of each car on one track 

 is opposite the ends of two cars of the other track, and each joined 

 by two couplings to the car in front of it on its own track, and in 

 the same way to the one behind it, and also to those diagonally in 

 front of it and behind it on the other track." Again, in speaking of 

 that startling process of egg development that makes the embryology 

 of Salpa one of the apparently insoluble problems of this branch of 

 inquiry, he says: " Stated in a word, the most remarkable peculiarity 

 of the Salpa embryology is this: It is blocked out in follicular cells, 

 which form layers and undergo foldings and other changes which 

 result in an outline or model of all the general features in the or- 

 ganization of the embryo. While these processes are going on the 

 development of the blastomeres is retarded, so that they are car- 

 ried into their final position in the embryo while still in a rudimen- 

 tary condition. Finally, when they reach the places they are to 



