G. GENERAL NATURAL HISTORY AND ZOOLOGY. 297 



to, " the associated zooids are always of two kinds. In one 

 (1) the zooid is destitute of all j^ower of true or sexual gen- 

 eration, and has as its proper function the general nutrition of 

 the colony ; (2) the other group of zooids has nothing to do 

 with the general nutrition of the colony; it has as its proper 

 function true generation, and the zooids which compose it 

 give origin to the generative elements ova or spermatozoa 

 either directly or after having first developed a special 

 sexual bud." For the former (1) the term trophosome is em- 

 ployed ; for the latter (2), gonosome (p. 23). 



The author adopts the subkingdom Coeleiiterata^ consider- 

 ing its introduction by Frey and Leuckart " an important 

 reform in zoological classification," and admits two classes 

 viz., Hydrozoa (having no stomach sac differentiated from 

 the general body cavity), with five orders, Hydroida^ Sipho- 

 nophora^ Lucernarice^ Discophora^ and Ctenophora ; and Ac- 

 tinozoa (distinguished by a stomach sac differentiated from 

 the general body cavity), with two orders, Zoantharia and 

 Alcyonaria. 



The special group monographed {Gymnohlastea) forms 

 one of the five suborders {Eleutherohlastea^ Gymiwhlastea^ 

 Ccdyptoblastea^ Monopsea^ and JRhahdophora) into which the 

 order Hydroidea is divided. Of the five suborders, one 

 {Uhabdophorci) is represented only by the fossil Graptolites. 

 The suborder Gymnohlastea is the most numerous in forms. 

 This suborder contains those hydroids developed from an 

 ovum through the intervention of a hydriform trophosome^ 

 whose zooids are invested in a " perisarc," and permanently 

 attached, and which are especially distinguished by the ab- 

 sence of hydrothecse or gonangia. The most familiar forms 

 on the American coast are Tuhidaria^ Syncoryne^ and ou- 

 yainvillia. In the monograph, twenty-one families are rec- 

 ognized and described, and forty-nine genera are combined 

 under them. Each family is characterized, first, by the pe- 

 culiarities of the trophosome^ and, second, by those of the 

 gonosome. The forms not found in British waters are indi- 

 cated by a triple asterisk {^^^ prefixed to the name. The 

 work is iHustrated by twenty-two plates, containing many 

 colored figures, and eighty-four wood-cuts in the text. 



N2 



