THE BAY OF BISCAY. 173 



more especially distinguished by the infinite varia- 

 bility of characters which in all other cases exhibit 

 the greatest constancy. In the Annelids the organs 

 of motion and of circulation vary in the most marked 

 degree in the different species. The respiratory 

 system is sometimes developed in an almost exagge- 

 rated manner, whilst in other cases it is found to 

 have completely disappeared, and that even in ani- 

 mals which are apparently very nearly allied to one 

 another. The nervous system itself, that system 

 which Cuvier characterised as the entire animal) pre- 

 sents no exception to this common law, for, in a spe- 

 cial memoir on this important question, I have been 

 able to demonstrate that this apparatus exhibits the 

 most singular variations. Thus I found in other 

 Tubicolous Annelids, and even in the Errantia, 

 these abdominal nervous chains cleft into two halves, 

 which were widely separated from each other ; while 

 on the other hand, I found in other species that this 

 same chain formed along the median line merely a 

 narrow and uniformly equal band, in the thickness of 

 which the ganglia seemed as it were embedded ; and 

 between these two extremes I moreover discovered 

 a great number of intermediate .forms. 



Thus those premature generalisations which have 

 more especially originated from the exclusive study 

 of animals belonging to a fixed type, vanish one by 

 one before an examination which is daily becoming 

 more and more severe ; and thus we learn day by day 

 more thoroughly to appreciate the scientific import- 

 ance of the study of the lower animals. In this respect, 

 botanists are in the same condition as zoologists. In 



