MODERN SYSTEMS.

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gether, naturalists make again the same mistake whichCuvier committed, when he associated the Helminthswith the Eadiates, only in another way and upon agreater scale. 1 The Bryozoa are as it were depauperatedMollusks , as Aphanes and Alchemilla are depauperatedEosaceae. Eotifera are in the same sense the lowestCrustacea ; while Helminths and Annelides constitutetogether the lowest class of Articulata. This class isconnected by the closest homology with the larval statesof Insects ; the plan of their structure is identical, andthere exists between them only such structural differencesas constitute classes. 2 Moreover, the Helminths arelinked to the Annelides in the same manner as the apodallarvae of Insects are to the most highly organized cater-pillars. It may truly be said that the class of Worms represents, in perfect animals, the embryonic states ofthe higher Articulata. The two other classes of thisbranch are the Crustacea and the Insects , respecting thelimits of which, as much has already been said above 3 asit is necessary to state here.

The classification of the branch of Articulata may,therefore, stand thus :—

1st Class: Worms ; with three orders, Trematods,(including Cestods, Planarise, and Leeches,) Nematoids,(including Acanthocephala and Gordiacei, ) and An­ nelides .

2nd Class : Crustacea ; with four orders, Eotifera,Entomostraca, (including Cirripeds,) Tetradecapods, andDecapods .

3rd Class : Insects; with three orders, Myriapods ,Arachnids , and Insects proper.

1 Compare Chap. II, Sect. 1, p.216. 3 Compare Chap. I, Sect. 18, p.

s Compare Chap. II, Sect. 2, p.219. 118-120.