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THE AMERICAN NATURALIST [Vol. XL VI 



supply to the heart of Limulus; and with the general structure 

 of the Ostracoderms. 



The experiments on functions of the brain recorded in Chapter 

 XI should be a valuable contribution to the interesting prob- 

 lem of metamerism as expressed through the activities of the 

 central nervous mechanism. 



Two defects in the descriptive matter are likely to interfere 

 with as extensive a utilization of the book by biologists as it 

 merits. The first to be mentioned is a want of directness and 

 definiteness in many of the descriptions that renders their com- 

 prehension extremely difficult, in some cases almost impossible. 

 This is due partly to the way references are made to the illus- 

 trations. Not infrequently a text description of a structure is 

 given, not very fully, in the course of which one or several 

 figures are referred to but without specifying the letterings for 

 the particular parts described. The reader, being in doubt, may 

 turn to the "Explanation of lettering" at the end of the vol- 

 ume, only to find that the illustrations in question either have no 

 letterings for the particular parts, or if sufficient patience in 

 digging is exercised, to find that the part is labeled with a dif- 

 ferent name from that used in the description. The account 

 of the "middle cord, the lemmatochord and the notochord" 

 (Chap. XVIII) is an example of the difficulty here indicated. 

 Although I have spent much time on this chapter, I have not 

 been able to get a clear understanding of what is dealt with. 

 How many distinct structures are in hand? "The beginning of 

 the notochord may be recognized in practically all segmented 

 invertebrates, as the so-called middle cord, or median nerve, and 

 m its derivative, the lemmatochord," p. 324. This statement is 

 general, t e , is not made as applying to any particular animal. 

 It seems definite to the effect that "median nerve" and "middle 

 cord are synonymous, and that the structure indicated gives 

 rise to the lemmatochord. But Fig. 224A, p. 327, representing 

 the ^ nerve cords and lemmatochord of Cecropia," presents to us 

 the late pupal stage showing the fully formed lemmatochord, 

 derived from the condensed sheaths of the median and lateral 

 cords; also remnants of the median nerve." (Italics by the re- 

 viewer.) In Limulus the "middle cord" is said, p. 334, to be 

 < arranged m two main lateral cords," and Fig. 55, U.ch., p. 67, 

 is reterred to as illustrating this statement. Turning to this fig- 

 ure and the explanation of letterings, we find that U.ch. stands 



