284 GLOSSARY. 



Monophyodont. When only one set of teeth is developed. 



Monoplast. A naked cell. 



Morphology. " The history of the modification of form which 

 the same organ undergoes in the same or in different organ- 

 isms" (Owen}. " The law of form or structure independent of 

 function" (Dallas). 



Morphone. A morphological element. 



Morula. " The multicellular blastosphere from which the gas- 

 trula is developed." 



Muffle. The naked part of the nose in the cow, dog, &c. 



Mutable types. (1) Those which have undergone modification of 

 structure during geological time ; they " all belong to the most 

 differentiated members of the classes " (Huxley}. (2) In modern 

 times there are numerous forms which, from inherent causes, 

 deviate from the parental type, " the whole organization," as 

 Mr. Darwin puts it, "having a tendency to vary." 



Myelon. The spinal cord. 



Myonine. The material of muscle. 



Myophane. A striated layer in Infusoria, supposed to represent 

 muscle. 



Myotomes. The vertical flakes of muscle in fishes. (Myotoma = 

 Myocomma of Owen.) 



Natural sekction is the theory that the " origin of species" is due 

 to the " preservation of favourable individual differences and 

 varieties, and the destruction of those which are injurious," 

 and in "the accumulation of innumerable slight variations, 

 each good for the individual possessor" (Darwin}. Geological 

 research, Mr. Darwin thinks, "does not yield the infinitely 

 many fine gradations between past and present species required 

 on the theory ; and this is the most obvious of the many objec- 

 tions which may be urged against it." Mr. Darwin further 

 observes that he has " probably attributed too much to the 

 action of natural selection or the survival of the fittest." Prof. 

 Mivart goes further, and asserts that " natural selection utterly 

 fails to account for the conservation and development of the 

 minute and rudimentary beginnings, the slight and insigni- 

 ficant commencements of structures, however useful these struc- 

 tures may afterwards become." It is, perhaps, scarcely neces- 

 sary to observe that the origin of species has nothing to do 

 with the origin of life. 



