304 EMBRYOLOGY AND CLASSIFICATION. 



another, and that their different modes of de- 

 velopment may lead from one to the other. 

 Thus far Embryology has not recorded one fact 

 on which to base such doctrines. 



In Radiates, as soon as the young is formed, 

 it is a spheroidal, radiated animal, exhibiting 

 from the beginning, in all the three classes of 

 this primary division, Polyps, Acalephs, and 

 Echinoderms, the general plan of structure so 

 characteristic of the Radiate type, and so distinct 

 from all others. Let us first see what inference 

 may be drawn from the development of the lower 

 representatives of this type ; even though I can 

 only allude here very generally to facts which 

 could not be stated more at length without a 

 great deal of illustration and detail. The young 

 Polyp reaches its mature condition through a 

 succession of changes, which, when compared 

 with the structural complication of the adult 

 representatives of the different orders in this 

 same class, promise 'to furnish better data for the 

 classification of these animals than have ever 

 been obtained heretofore. The various modes 

 of increase observed among Astra3ans, and espe- 

 cially among Fungidae, already show that the 

 families in which independent animals complete 

 their growth, without forming compound com- 

 munities, are inferior to the compound ones ; 

 while those in which one diameter prevails over 



