366 



PROVISIONAL HYPOTHESIS Chap. XXVII. 



I 



quagga and Lord Morton's mare, affecting the ovarium of the 

 female, so that the ovules and offspring subsequently produced 

 by her when impregnated by other males are plainly affected 

 and hybridised by the first male. 



Development.— The fertilised germ reaches maturity by a vast 

 number of changes : these are either slight and slowly effected, 

 as when the child grows into the man, or are great and sudden, 

 as with the metamorphoses of most insects. Between these ex- 

 tremes we have, even within the same class, every gradation : 

 thus, as Sir. J. Lubbock has shown, 13 there is an Ephemerous 

 insect which moults above twenty times, undergoing each time 

 a slight but decided change of structure ; and these changes, 

 as he further remarks, probably reveal to us the normal st( 



to 



a 



of development which are concealed and hurried through, 

 or suppressed, in most other insects. In ordinary metamor- 

 phoses, the parts and organs appear to become changed into the 

 corresponding parts in the next stage of development; but 

 there is another form of development, which has been called by 

 Professor Owen metagenesis. In this case "the new parts are 

 " not moulded upon the inner surface of the old ones. The 

 " plastic force has changed its course of operation. The outer 

 " case, and all that gave form and character to the precedent 

 " individual, perish and are cast off ; they are not changed into 

 " the corresponding parts of the new individual. These are due 

 " to a new and distinct developmental process," &c. 14 Metamor- 

 phosis, however, graduates so insensibly into metagenesis, that 

 the two processes cannot be distinctly separated. For instance, 

 in the last change which Cirripedes undergo, the alimentary 

 canal and some other organs are moulded on pre-existing parts ■ 

 but the eyes of the old and the young animal are developed in 

 -tirely different parts of the body ; the tips of the mature 



are formed within the larval limbs, and may be said 

 metamorphosed from them; but their basal portions 

 and the whole thorax are developed in a plane actually at 

 right angles to the limbs and thorax of the larva ; 



ISfiV Tl rr Ct ' Liim * S ° C "' V01, XXiVM ° n this Sub J' ect ' ia reference t0 the de - 

 S <£ 71 • . -.o^ velopment of star-fishes, and shows how 



9« v°? ^ f T 8 ' 849 ' PP> 25 " CUriousl y metamorphosis graduates into 



, J ^ J haS S ° me excellent gemmation or zoid-formation, which is 

 remarks (< Medical Times,' 1856, p. 637) in fact the same as metagenesis. 



limbs 

 to be 



and 





