AMERICAN HYDROIDS. 



SECTION -2. TIT K s KI rnn ,A i f i T>.K. 



AI()RIMI()L()(;V OF THE SEETTTLAHID^E. 



As indicated in the first part of this work 1 it is the intention to defer the general discussion 

 of the morphology of the order to the last part. In accordance with this plan nothing will 

 he discussed here except those structures which uiv peculiar to the Sertularidffi, or those which, 

 while shared by other forms, still furnish peculiarities upon which diagnostic features can be 

 liased. In the former category will be included the opercuhnn. although this structure is found 

 in the Campanulinidee, and under the latter head will be discussed other features, particularly 



the stem, the h ydranths. the hydrothec:e. and thegonangia. 



A little study will make it evident that the Sertularidse contain few characteristic structures. 

 at least, as compared with the Plumularidse, and that the family is therefore lower in the 

 zoological scale." It has then-fore not received the attention from the morphologists that has 

 been paid other groups. Indeed, it appears to have received less careful study than any of the 

 other large groups of the Hydroida. and there are surprisingly few papers that more than touch 

 on the morphology of this family. At first sight this seems rather strange, e-pecially when we 

 remember that this is the longest known and most familiar family of the order. This lack of 

 interest is probably due mainly to the following reasons: 



Fli'xt. The earlier naturalists were nearly all of them systematists rather than morphologists, 

 and studied the more supcrticial characters. 



S.i'miil. When effective morphological investigation became practicable by the introduction 

 of microscopical and histological technic, investigators became interested in the larger forms 

 with larger and more conspicuous hydranths, as in the gymnobla.-t ic forms, or the beautiful and 

 wonderful medusa' attracted their attention, and their investigations were thus led to the colonic- 

 which produced the free medusa-; or the neinatc iphores and conspicuous features of the gonosome 

 of the Plumularidse lured the student to the scrutiny of these intensely interesting structures. 



Third. Such investigations as have just been referred to led to a general understanding of 

 the morphology of the Hydroida as a whole, and, as the Sertularida- oli'eivd little that appeared 

 to be novel, thai family was naturally passed by in favor of groups oil'ering more interesting, 

 because more novel, structures for investigation. 



The. writers who have contributed most to our knowledge of the morphology of this family, 

 purely systematic work being excluded, are the following: Louis Agassi/, who gives an excellent 

 and superbly illustrated account of X rtnLir'ni /uniiilir.' Allman.' who di-cu^-es the gonosoine of 



1 American Ilydn.ids. 1'art I, The I'lumularid:, . I '.inn, ].. :',. 



* While this is true \vlirn tin- Scrtularidic ami l'lunmlarid;i- an- compared, ii liy no means follows that the 

 Se rti i la rid: e are of low rank u hen nun pared \\ ith the hydroids in _'cin-ral. Indeed. i|iiile the opposite i< true if \vi- 



admit the view now very generally adopted -that the sessile gonophores represent iK-.Tailfl ineclii.sr. This 



however, will he di-i-nssc-d later. 



M'onlrilmtionsto the Natural History of tin- I'nited State-. IV. l.siii'. p. 326. 



'Monograph of the Gymnoblastic Ilydroids. 1S71, \>. ">n. 



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