PRINCIPAL SYSTEMS OF ZOOLOGY 259 



standards also to the minor divisions of the animal kingdom, down 

 to the genera and species, and to do this for every class singly, with 

 special reference to the works of monographers. But this is such an 

 herculean task, that it can only be accomplished by the combined 

 efforts of all naturalists during many years to come. 



seems to me also that, though not entirely neglected, the history of the fossil remains 

 is not sufficiently prominent, and the manner in which they are frequently presented, 

 without connection with the living types, is particularly unfavorable to a true appre- 

 ciation of their natural relation to their living representatives. The time has truly 

 come when the whole Animal Kingdom should be represented in its development 

 through all geological periods as fully as the mode of growth of the living is, in our 

 days, connected with their general history. 



Ilespecting the classes [in Van der Hoeven's classification], I believe, for reasons al- 

 ready stated, that the Infusoria ought to be divided off according to their natural 

 affinity, partly among the Algae, partly among the Worms, and partly among the 

 Bryozoa. The relation of the Rhizopods to the lower Algae and especially to the Coral- 

 lines seems to me daily more probable, and I consider the evidence thus adduced of 

 the vegetable character of the Anentera as amounting almost to a demonstration. 



In the class of Acalephs, the Ctenophorae occupy a position inferior to the Disco- 

 phorae. It seems to me hardly questionable that they should occupy the highest posi- 

 tion in that class. The Sipunculidae, which I am inclined to refer to the class of 

 worms, are included among the Echinoderms. The ambulacral system, with or without 

 external suckers, constitutes the essential character of the Echinoderms. Sipunculus 

 has none. The distinction of the intestinal worms and the Annulata as two distinct 

 classes, separated by the Rotatoria, seems to me unnatural. The Turbellaria and Suc- 

 toria unite the Annulata with the Trematodes and other worms as one class, and the 

 most recent investigations show unquestionably that the Rotatoria are Crustacea. It 

 seems to me also unnatural to separate the insects and spiders as two classes. The 

 Tardigiada and Acarina form the transition to the Podura and Epizoa. The class of 

 Crustacea, though well defined if we add the Rotatoria to it, should be placed below 

 the insects. The general classification of the branch of Mollusks appears the least satis- 

 factory in this work, for while the Tunicata are considered as a distinct class, and the 

 Conchifera as another, including the Brachipods, the class of Mollusca proper includes 

 not only the Pteropoda and Gasteropoda, but also the Cephalopoda. Evidently, the 

 Cephalopoda are brought here into too close connection with the Gasteropoda. A 

 fuller consideration of the fossil Cephalopoda would easily have satisfied the author 

 that these animals constitute for themselves an independent class. 



Since the publication of the Animal Kingdom of Cuvier, Van der Hoeven's Text- 

 book is the only general work on Zoology in which the class of fishes is presented in 

 a manner indicating a thorough acquaintance with this class of animals. The treat- 

 ment of the other Classes of Vertebrata is equally deserving of praise. 



