220 Professor Clark on a Case 



drew the attention of those engaged in them, to the consideration 

 of those unusual or imperfect forms of animals which had hitherto 

 been considered to defy subservience to general laws, and which 

 bad been collected in a heterogeneous mass, as objects of igno- 

 rant curiosity, or as proofs that nature is sometimes capricious, 

 and disdains an absolute submission to those forms which she 

 herself had consecrated. An extended enquiry soon led to the 

 conclusion that all the known aberrations from usual standards 

 may be referred to one of three orders: according as they are 

 characterized by defect, or by excess in the development, or by 

 the inversion of parts. With respect to anomalies from defect, 

 it was further ascertained that those organs in which they occur 

 have been arrested in some one of those transient stages through 

 which they were passing to a higher degree of perfection : and 

 that in these stages they resemble the permanent condition of the 

 perfect organ in some lower order of animals*. The explanation 

 of the two other orders has not hitherto been so satisfactory. 

 With respect to excess of development, though it has been clearly 

 determined, that no organ in an individual of a lower class, how- 

 ever it may deviate from its perfect type, ever represents the type 

 of a higher class : yet, the various instances of this mode of de- 

 viation have seemed so entirely to militate against general rules, 

 that some distinguished anatomists have considered each case as 

 forming a genus of itself, and as subject from its earliest period 

 to its own peculiar laws. May it not be, however, that in the 

 production of these unusual animal forms, the law appears to be 

 peculiar merely because its ordinary expression or effect, has 

 been disturbed by causes which it is very difficult to assign, and 



* In a great many instances also the cause of the arrest has been assigned. 



