x ii SYNOPSIS OF 



According to St. Hilaire a species is a collection or succession of individuals 

 characterized by a combination of distinctive features, the transmission of which is 

 natural, regular, and indefinite in the existing order of things." 



MM. Eay and Drouet {Revue et Mag. cle Zoologie, 1849) give their views of 

 what forms a species in the following terms : " Generalement on entend, par se mot 

 (espece), un type d'organisation de forme et d'activite, rigoureusement determine, 

 qui se perpetue successivement par generation directe et d'une maniere indefinie avec 

 la meme Constance de caracteres." 1 



Milne Edwards's definition of species, I think, is less clear. He says : " On 

 donne le nom d'espece a la reunion des individus, qui se reproduisent entre eux avec 

 les meraes proprietes essenticlles." 



Cuvier considered that the fact of the succession and of the constant succession, 

 constituted alone the validity of the species. 



Dr. Morton comprised his view of species as "a primordial organic form." 



Neither of these definitions fulfils my own idea of what forms a species. It 

 seems to me that a species must be considered to be a primary established law, stamped 

 with a persistent form (a type), pertaining solely to itself, with the power of suc- 

 cessively reproducing the same form and none other. 



Blainville, in his Manuel de Malacologie, divides the Unionidce (his Siib-Mgtilacea) 

 into Anodonta and Unio, but thinks that species will be found which will make these 

 to be united. 2 



Dana 3 says "a species corresponds to a specific amount or condition of concentred 

 force, defined in the act or law of creation.'''' 



Sowerby says : " The difficulty of ascertaining to which genus of Lamarckian 

 Naiades certain species belong, arises from the very general similarity of form," &c. ; 

 "in fact, an examination of a sufficient number of species will prove that no depend- 

 ence can be placed upon the characters by which authors usually attempt to discrim- 

 inate between these genera, and that the transition from one to another is so gradual 

 in some instances, and so strongly marked in others, that it is not surprising that 

 authors, Avho, having only met with certain species, and not being aware of such 

 intermediate links, should have considered them as the types of new genera." 1 And 

 further: "We think we have already said enough to prove that, unless it be thought 



1 M. Drouet, in his Etudes sur les Nayades de la France, 1854, has given valuable observations on 

 the anatomy, function, diagnosis, &c. of Anodonta. 



2 See page 540. 



3 Thoughts on Species. Am. Jl. of Science, 1857. 



4 Zool. Journ., vol. i. 



