LITERARY NOTICES. 



273 



Space will not permit us to further notice 

 the special points elaborated by the author, 

 the table of contents alone occupying two 

 crowded pages. The wotk is divided into 

 four parts : I. A general account of the life- 

 history of salpa. II. The systematic affinity 

 of salpa in its relation to the conditions of 

 primitive pelagic life ; the phylogeny of the 

 Tunicata ; and the ancestry of the Chordata. 

 III. A critical discussion of my own observa- 

 tions and those of other writers, on the sex- 

 ual and asexual development of salpa. IV. 

 On the eyes and subneural gland of salpa, 

 is by M. M. Metcalf, who, among other 

 points claims, contrary to Buetschli, that the 

 eye of salpa is not homologous with the eye 

 of any other chordate animal. 



The general reader and biologist will be 

 especially interested in the views presented 

 in Part II. Brooks speaks of the wonderful 

 scarcity of pelagic life in the lagoons and 

 landlocked waters of the Bahamas, and ex- 

 plains it by the theory that the surface life 

 is eaten up by the animals at the bottom, 

 every organism swept in by the tides and 

 every larva born in the sounds being eaten 

 up by the polyps, etc., at the bottom, the 

 competition for food being so fierce. He 

 maintains that early in the Cambrian period, 

 or when life first began, it was pelagic, or 

 confined to the surface. Gradually some of 

 the pelagic forms, at first mmute and sim- 

 ple, settled at the bottom, and such a primi- 

 tive bottom fauna was similar to the lower 

 Cambrian fauna. This bottom fauna at 

 first entirely depended for food upon the 

 pelagic life at or near the surface, there be- 

 ing no plant life yet in existence. This 

 primitive bottom fauna was established 

 around elevated areas in water deep enough 

 to be beyond the influence of the shore. 

 He claims that the great groups of Metazoa, 

 or all animals above protozoans, were rapidly 

 established from pelagic ancestors. This, it 

 may be said in passing, is in direct opposi- 

 tion to the view generally entertained that 

 the pelagic fauna is derived from the shoal- 

 water or shore life. 



After the establishment of the first bot- 

 tom fauna competition swiftly arose, became 

 very rigorous, and led to rapid evolution, and 

 " life on the bottom introduced many new 

 opportunities for divergent modification and 

 for the perfecting of animals." The in- 

 TOL. XLV. 22 



crease in size of the animals also increased 

 the possibilities of variation, and led to the 

 natural selection of those peculiarities which 

 increased the efficiency of different organs, 

 and thus proved an important factor in the 

 evolution of complicated organisms ; the 

 new modes of life what they were, the au- 

 thor does not state, but they must have been 

 in great part the results of fixation at the 

 bottom, together with the operation of cur- 

 rents, etc. permitting the acquisition of pro- 

 tective shells, or hard, supporting skeletons. 

 Life at the bottom also introduced the factor 

 of competition between blood relations, the 

 fiercest competitors of each kind of animal 

 being its closest allies, " which having the 

 same habits, living upon the same food, and 

 avoiding enemies in the same way, are con- 

 stantly striving to hold exclusive possession 

 of all the essentials to their life." Thus 

 the tendency of such bottom forms was to 

 divergent evolution of the great types of 

 animal life. Since then, the author claims, 

 " evolution has resulted in the elaboration 

 and divergent specialization of the types of 

 structure which were already established, 

 rather than in the production of new types." 

 This is all very likely, and, to continue the 

 train of reasoning, the next great step was 

 the origin of land animals, terrestrial and 

 fresh-water arthropods, and the third great 

 step was the evolution of animals, arthropod 

 and vertebrate, adapted for life in the air. 

 We may suggest that it was the Lamarckian 

 factors of profound and widespread changes 

 in the environment, such as a transfer of 

 the habitat of animals from the surface to 

 the ocean bottom which tended to increase 

 and diversify life forms, together with the 

 use and disuse of organs resulting from 

 enforced adaptation to the new conditions. 

 After all this had begun there comes in the 

 more passive factor of natural selection, 

 subordinate, though constantly at work, 

 which further promoted the elaboration and 

 specialization of organic forms. 



Letters of Asa Gray. Edited by Jane 

 LoRiNG Grat. In Two Volumes. Bos- 

 ton : Houghton, Mifflin & Co. Price, $4. 



Dr. Gray was a delightful correspond- 

 ent. He wrote with the easy manner and 

 hearty tone that give letters then- highest 

 charm. In telling distant friends what he 



