348 PROCEEDINGS OP THE AMERICAN ACADEMY. 



markings, organs, and structures developed, and for the time being 

 useful only to become at a later stage useless and therefore discarded, 

 as new and dissimilar conditions of life arose, — it seems almost self- 

 evident that such markings and structures were the result of the re- 

 sponses of an organism in its most plastic time of life to changes in 

 its habits, such changes being due either to changes in its surround- 

 ings, or to the effort to repel the attacks of insects, birds, etc. 



However such stages arose, they are at the present epoch trans- 

 mitted from parent to offspring with wonderful certainty. Among 

 the Arctians, and in other caterpillars, the number of moults is known 

 to vary, either from artificial breeding or from other unknown causes, 

 possibly lack of nutrition. This form of heredity was called by Dar- 

 win* ''Inheritance at corresponding Periods of Life," and by Haeckelf 

 " Homochronous Transmission." Darwin thus describes the phenome- 

 non : " When the embryo leads an independent life, that is, becomes 

 a larva, it has to be adapted to the surrounding conditions in its struc- 

 ture and instincts, iudepeudently of those of its parents ; and the 

 principle of inheritance at corresponding periods of life renders this 

 possible." (p. 51.) Again: "On this principle of inheritance at 

 corresponding periods, we can understand how it is that most animals 

 display from the germ to maturity such a marvellous succession of 

 characters." (p. 60.) 



Examples of this law are the complicated metamorphosis of certain 

 free, but more especially the parasitic worms, notably the fluke worms 

 and the Cestodes, the complicated metamorphoses of the Echinoderms, 

 of the Mollusca, the Crustacea, and the metamorphic insects, and more 

 especially such insects as the Meloidae, Rhipiphoridai, and Stylopitke, 

 in which there is a hypermetamorphosis. 



It is not altogether improbable that the phenomena of alternation 

 of generations is primarily due to changes in surroundings, and hence 

 of habits, resulting in new needs which were met by adaptation to 

 the new surroundings, the different stages being finally fixed by 

 homochronous heredity. Take the case of the Hydroids, where the 

 generation of fixed hydra-like individuals gives rise by budding to the 

 free-swimming, egg-producing medusa form. The hydra-like indi- 

 viduals are the result of direct inheritance, while the medusa is prob- 



* The Variation of Animals and Plants under Domestication, II. 51. 



t History of Creation, I. 217, 218. See also Giard, wlio, referring to the 

 laws of heredity, remarks: " Plusieurs de ces lois, et en particulier la lot de 

 l'heredite homoehrone, fournissent aussi, nous le verrons, de bons arguments en 

 faveur du principe de Lamarck." Revue So., 6 Dec, 1890. 



