CLASSIFICATION. IX 



into a single Class. Other deviations of form arise un- 

 doubtedly from intra-uterine disease, and certain abnormal 

 forms of nutrition give rise to dwarfs and giants ; these 

 have been arranged in three Classes Diseases, Arrests, 

 and Excesses of Growth. Two great Classes of malfor- 

 mations remain Arrests of Development, which are con- 

 nected with variations on the one hand and with diseases 

 on the other ; and Double Conditions, either of the whole 

 organism or of a limb or part, concerning the nature of 

 which much difference of opinion exists. 



The- following six Classes have therefore been adopted in 

 the arrangement of the Teratological Collection : 



Class I. Variation. 

 II. Duplicity. 



III. Excess of Growth. 



IV. Arrest of Growth. 



V. Arrest of Development. 

 VI. Disease. 



These great divisions, as has been already indicated, are 

 by no means to be looked upon as certainly fixed; they 

 are convenient groupings together of phenomena which are 

 apparently related to each other. Analogy leads us to sus- 

 pect that the causes in each Class are similar ; but further 

 investigation may lead to a redistribution of some groups, 

 and perhaps to some alterations in the number and nomen- 

 clature of the classes themselves. 



Although the above-enumerated Classes are used as 

 the basis of classification in this Catalogue, it has been 

 found convenient to make them subservient to an artificial 

 grouping of the preparations in the following order : 



Series I. Abnormal conditions in Plants. 



II. Abnormal conditions of the Axis in Animals. 



III. Abnormal conditions of the Limbs. 



IV. Abnormal conditions of the Skin and its Ap- 



pendages. 



