The Principles of Palaeontology. 167 



apparent reason, groups flourish and then irrevocably disappear, 

 after having presented characteristics which have been compared 

 to the degeneration of old age. There would then be a vital 

 force for the species and higher groups as for the individual, and 

 the lifetime of such a form would be limited, as is that of an 

 individual. 



Against this hypothesis serious objections can be raised. The 

 characters compared are not of the same order. Instead of look- 

 ing to the higher races of animals where reproduction takes 

 place by means of the Qgg^ it would be more reasonable to look 

 for our terms of comparison, for example among the Zoophytes 

 or Protozoa, where increase takes place by the division of the 

 individual itself into two parts. It is indeed just in this way, 

 by a sort of division, that species multiply. Nothing is more 

 indefinite than the notion of old age among such animals, where 

 death seems only to arrive through some accidental cause. 

 (Weismann, Neumayr.) 



But at the same time there exist groups which seem endowed 

 with an indefinite longevity ; from the most ancient epochs they 

 have perpetuated themselves with very slight variations. The 

 Brachiopoda, for instance, have changed so little that the genera 

 from the Cambrian [Ordovician] are still existing. The differences 

 between the oldest form known, Lingulella, and a Lingula of the 

 present day, are quite insignificant, and the Lingulas, properly so 

 called, together with the Discinas, have existed' almost without 

 modification since the Cambrian [Ordovician] epoch. The same 

 may be said of the articulated Brachiopoda, such as the Tere- 

 bratulas and the Ehynchonellas. There is no Brachiopod, in 

 fact, at the present epoch which has not had almost identical 

 representatives from the earliest palaeozoic periods.* 



* [Recent study of the generic evolution of the Brachiopoda does not confirm these statements. No 

 evidence cculd be more conclusive than that now public of the rise, culmination and decline of a 

 very large number of generic groups both of the inarticulate and articulate Brachiopods. Lingala, 

 Crania and perhaps Rhynchonella do, indeed, represent types of great stability and vigor, which 

 have perpetuated themselves through geologic time with the minimum of variation ; they are not 

 merely remarkable cases among the Brachiopods, but they are exceptional instances among organ- 

 Isms generally. But it is not difficult to point out structural features wherein the recent forms of 

 these genera differ from their early representatives, even though such differences be not now 

 regarded of generic consequence. The final statement of the above paragraph could not be more 

 erroneous, and it is most unfortunate to find it promulgated here. None of the existing types of 

 Brachiopods were present in the earliest palaeozoic periods; not more than f wo generic types have 

 continued from the palaeozoic to the present, and it is safe to say of existing Brachiopods generally 

 hat they are for the most part highly complicated culminant forms or simple decadent expressions 

 of types introduced during the post -palaeozoic and later periods of the earth's history.— Ed . ] 



