188 



CLASSIFICATION. 



r Generative ele- 

 ments discharg- 

 ing themselves 

 externally 



9. 



No stomach-sac^ 

 difl'erentiated | 

 from the gene- ^ HYDROZOA 

 ral body-cavity j 



Locomotion never 

 by bands of vi- ^ 

 bratile lamellae 



Generative ele- 

 ments discharg- 

 ing themselves 

 into the body- 

 cavity 



Never with a hydriform"^ 

 trophosome united with 

 the gonosome into a nata- 

 tory colony (woodcuts, 

 figs. 6-1-G7) J 



Always with a hydriform ^ 



trophosome united with j 



the gonosome into a nata- I 



tory colony (woodcut, fig. | 



I 68) J 



f Generative elements in sym-~) 

 metrically disposed, longi- 

 tudinal, band-like projec- 

 tions of the inner surface 

 of the somatic cavity. Body 

 stalked, fitted for attach- 

 ment (woodcuts, figs, 71, 

 7-2) 



Generative elements formed ^ 

 in symmetrically disposed, 

 pouch-like dilatations of 

 the somatic cavityofabody ^ 

 which is not stalked and 

 not fitted for attachment 

 (woodcuts, figs. fi9, 70) 



A stomacl>-s.ic ^ 



differentiated I 



from the gene- f 



i ralbody-cavity J 



ACTINOZOA 



Locomotion always ^ 

 by bauds of vi- 

 bratile lamellae 

 (woodcuts, figs. 

 73, 74) 



Tentacles subuliform ; symmetry for 

 the most part hexameral (woodcuts, 

 figs, e-i, 03) 



Tentacles leaf-shaped, with the raar- 

 '-- gins cirrated ; symmetry tetrameral 



HVDKOIUA. 



SiPHOXOPHOK.V. 



LUCERN.\RI.E. 



Ctexophora. 



ZOANTHAKIA. 



When the various living forms included under the order Hydroida are compared with one 

 another, it will be found that they present among them four principal modifications, and these afford 

 grounds for the subdivision of the living representatives of the order into four sub-orders; while, if we 

 include the graptolites, a fifth sub-order must be established for the reception of these extinct organisms. 



Confininf' ourselves for the present to the living hydroids, we find that three out of the four 

 sub-orders under which they are included possess a hydriform trophosome, which, in the develop- 

 ment of the hydrosoma, intervenes between the ovum and the generative buds, whose assemblage 

 constitutes the gonosome. In the fourth sub-order there is no hydriform gonosome, and tlie ovum 

 becomes developed by direct metamorphosis into a medusifonn hydrosoma, to which is assigned 

 the performance of generative as well as nutritive functions. 



