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SCIENCE 



[N. S. Vol. XXVIII. No. 725 



terata)." And the figure of hydras on pond- 

 weed is inverted, giving one the impression 

 that animals are grov^ing on the stems up in 

 the air. 



In the chapter on Echinoderms the follow- 

 ing sentences are from one point of view 

 very instructive : " The sand dollars are 

 lighter colored than the sea urchin. Why ? " 

 Here the bright pupil is probably expected to 

 hold up his hand and, without ever having 

 seen a sand dollar, much less observed one in 

 its natural habitat, explain the matter, after 

 the common fashion, as a case of protective 

 coloration. The explanation fits the case all 

 the better if it is not known that many species 

 of sand dollars when alive in the water and 

 still containing a large amount of purple pig- 

 ment are anything but light colored and do 

 not become so until they are bleached out or 

 denuded of spines or both. " Starfish," the 

 author tells us, " are brown or yellow. This 

 makes them inconspicuous on the brown rocks 

 or yellow sands of the seashore." In this as 

 in several other cases the author seems naively 

 unaware of the danger of making general 

 statements on the basis of a few instances. 

 Only a slight investigation of the colors of 

 different starfish would make him acquainted 

 with species of red, orange, purple or other 

 color of the most conspicuous kind, and would 

 doubtless have shaken his faith in the general 

 occurrence of protective coloration in this 

 group. The flat form and light thin walls of 

 the sand dollars are explained as an adapta- 

 tion to prevent their sinliing into the sand. 

 This may be the case, but the author is a little 

 venturesome when he relates that " the five- 

 holed sand cake or sand dollar has its weight 

 still further diminished by the holes, which 

 also allow it to rise more easily through the 

 water." Whether he conceives these creatures 

 to have the faculty of rising and swimming 

 about like fishes is not entirely clear, but the 

 possession of some means of locomotion above 

 the bottom seems to be implied. 



In regard to the common earthworm whose 

 structure is correctly described in so many 

 text-books it is surprising to find the author 

 falling into several errors. The eggs are said, 

 on page 46, to pass out of two pairs of open- 



ings in the fourteenth and fifteenth segments, 

 while on page 47 they are said to pass into the 

 collar-like case as it passes the fifteenth and 

 sixteenth segments — two contradictory state- 

 ments, neither of which is correct. A struc- 

 ture marked ES in Fig. 77 is called egg 

 gland, while other bodies marked o^ and o 

 occurring in the twelfth and thirteenth seg- 

 ments respectively are not given any further 

 explanation. The word clitellum is employed 

 for the chitinous capsule which surrounds the 

 eggs instead of the glandular region of the 

 body by which the capsule is secreted. 



After warning us that " the name ' worm ' 

 is often carelessly applied " and that it should 

 be given " only to segmented animals without 

 jointed appendages " we are given a classifica- 

 tion of the " four classes in the branch 

 Vermes," two classes of which, the round- 

 worms and the rotifers, are not segmented 

 forms at all, while in the third class, the flat- 

 worms, segmented forms occur only in one of 

 the subordinate divisions. The first class is 

 designated " earthworms, including sand- 

 worms and leeches," which is something of a 

 sacrifice of accuracy to simplicity of termi- 

 nology. 



On page 79 we meet with the statement 

 that: 



It is probable that the large or compound eyes 

 of insects only serve to distinguish bright objects 

 from dark objects. The simple eyes afford distinct 

 images of objects within a few inches of the eye. 



It would be difficult to give an account niore 

 at variance with the facts, and we recommend 

 the perusal of Forel's " Experiences sur les 

 Sensations des Insectes " before the issue of a 

 second edition. On the same page occurs a 

 section upon " Inherited Habit or Instinct," in 

 which the mode of origin of instincts is de- 

 scribed and summarized in the sentence " Re- 

 peated acts constitute a habit, and an inherited 

 habit is called an instinct." We do not criti- 

 cize the writer for espousing a view of the 

 origin of instincts now largely discredited and 

 accepted by practically none in the unqualified 

 form here set forth, but if the subject is dis- 

 cussed at all the student should not be given 

 but one interpretation and taught dogrdatically 

 that it is the correct one. The table for classi- 



