August 13, 1909] 



SCIENCE 



217 



Fourth, senescence is at its maximum in the 

 very young stages, and the rate of senescence 

 diminishes with age. 



As the corollary from these, we have this — nat- 

 ural death is the consequence of cellular differ- 

 entiation. 



Those interested in education will find in 

 this last chapter a fine statement of rapid 

 mental growth of the infant. 



Clearly in ultimate analysis the growth of 

 an organism is but a small factor in the prob- 

 lem of its entire life. At a guess, the energy 

 expended in growth is to the entire energy 

 output of the organism as one to one thousand. 

 It should also be remembered in this connec- 

 tion that all the material which enables the 

 embryo to grow so fast at first is a function of 

 the adult life work of the parents. An adult 

 hen may lay 200 eggs in a single year, the 

 materials of which may enable 200 chicks to 

 complete 98 per cent, of their growth at hatch- 

 ing. 



C. F. Hodge 



Clark Univeesitt 



The Development of the Chich: An Introduc- 

 tion to Emhryology. By Frank K. Lillie. 

 Pp. xi + 472. 251 Figs. New York, Henry 

 Holt and Company. 1908. 

 The intention of the author of this book is 

 to present in a simple, straightforward way 

 the essential facts of the development of the 

 chick for the use of beginners in embryology. 

 This purpose has been to a very large degree 

 realized, despite the ever-present temptation 

 to enter into comparative discussions. 



The book is divided into two sections, the 

 first of which is devoted to a description of the 

 formation of the embryo and is to an excep- 

 tional degree original and excellent. The 

 second part, consisting of eight chapters on 

 the development of the organ systems from the 

 beginning of the fourth day of incubation to 

 hatching, occupies a little more than half of 

 the work. 



The introduction is a statement of certain 

 embryological theories and facts of general in- 

 terest which can not properly be included in 

 the body of the book. 



The first chapter is a description of the 



structure, chemical composition and forma- 

 tion of the egg. 



So little is known of the processes which oc- 

 cur while the hen's egg is in the oviduct that 

 a consistent account of them is impossible. 

 Consequently, Dr. Lillie in the second chapter 

 bases the description of the development before 

 laying, which includes the fertilization, ma- 

 turation and cleavage of the ovum, and the 

 formation of the ectoderm and entoderm, upon 

 the work of Harper, Patterson and Blount 

 upon the egg of the pigeon. This is an un- 

 avoidable exception to the author's rule of 

 limiting the description to the development of 

 the chick. 



The third chapter contains a variety of 

 material such as an outline of develop- 

 ment, a statement of the orientation of 

 the embryo in the egg, a discussion of the 

 methods of classifying embryos, and an ex- 

 cellent table of the time of appearance and 

 rate of differentiation of the organs. It would 

 be wiser, perhaps, to omit this chapter because 

 it makes too great a break in the account of 

 the development of the embryo and contains 

 much that the student can not yet understand. 

 The content of the chapter could well be 

 used elsewhere: for example, the section on 

 orientation should be used, I believe, in con- 

 nection with the account of the formation of 

 the entoderm, given in the preceding chapter. 

 The table, being merely for reference, should 

 be used as an appendix. 



The fourth chapter, entitled, From Lay- 

 ing to the Formation of the First Somite, 

 is divided into four sections. The first is 

 a description of the blastoderm in the un- 

 incubated egg and amounts to a review of 

 the latter part of the second chapter. The 

 primitive streak is described in the second sec- 

 tion under four heads : Whole Views, Sections, 

 The Head Process and Interpretation of the 

 Primitive Streak. This division, especially 

 the separation of the description of the whole 

 views from that of the sections of the primi- 

 tive streak, seems unwise. Four views of the 

 blastoderm and three sections of the primitive 

 streak of the sparrow, copied from Schauins- 

 land, serve only to show by contrast the excel- 



