AND THE LOWER ANIMALS. 221 



Of those who went still farther, the greater number, 

 and, among others, two distinguished English ento- 

 mologists, Messrs. Kirby and Spence,* asserted that a 

 single intercommunication of the sexes was adequate 

 to the fecundation during several generations of all 

 the families which resulted from this union. Some, 

 and among them Leon Dufour, the distinguished anato- 

 mist of Saint- Sever, boldly had recourse to spontaneous 

 generation, in order to explain this remarkably ex- 

 ceptional fact.f Others again, as M. Morren, admitting 

 that this opinion was not in unison with modern 

 science, supposed that generation occurred through 

 the individualization of a previously organized tissue. % 

 The first of these hypotheses either explained nothing, 

 or assumed the existence of a complete organic ap- 

 paratus, which was not present. As to the theories 

 which in a greater or lesser degree were based on the 

 spontaneous generation doctrine, we know that at 

 the present day they are inadmissible. Besides, all 

 these doctrines applied to a special case, which till 

 then had been regarded as without an analogue, and 

 for that reason, must fall before the multiplicity and 

 exceeding complexity of the phenomena now known. 



In discovering the alternation of form and condition 

 presented by each species of Salpa, Chamisso — and 

 to say so is but to do him a justice that has not been 



* " Introduction to Entomology." 



f " Recherches sur les Hemipteres," 1853. — Annales des Sciences 

 naturelles. Leon Dufour, who passed his life in the little town of 

 Landes, published works on the anatomy of insects, which very 

 soon attained great repute. 



% "Memoire sur Immigration du Puceron du Pecher (Aphis 

 persicce) et sur les Caracteres et 1' Anatomic de cette Espece," 1836. 

 — Annales des Sciences naturelles. 



