12 AMERICAN HVDEOIDS. 



In regularly branching species of campanularians the gonangia are usually bom on the 

 stem and larger branches, often bemg placed in the axUs of branchlets or pedicels. In forms 

 Towuio' from a creci>iiig ]-ootstock the gonangia often spring from the rootstock itself, without 

 reference to the position of the pedicels. 



Perhaps the simplest form of gonangium is the oblong-oval without distinct collar or neck, 

 such as Camfanularia veHidllata (fig. 55) or C. inconspicua, or C.jlexuosa (fig. 61). The first 

 departure from this primitive form is iu the production of a collar at the distal end, which is low 

 and mconspicuous m Obelia comm.issuralis (fig. 48) and several other species of the same genus, 

 and forms a rather conspicuous everted collar iu Olytia noliformis (fig. 49). The beguming of a 

 tubular "neck" is found in Camfanularia urceolata, and this neck becomes long, tubular, and 

 somewhat curved in such species as Campanularia fusiformis (fig. 57) and C. magnifica (fig. 54). 

 In the Campanularidse, as in many Sertularidse, we find numerous instances of more or less 

 conspicuously annulated gonangia. These anntdations may appear simply as large, irregular 

 rugosities, as ia Clytia noliformis and C. universitatis, or as numerous and beautifully sym- 

 metrical annulations, as in Clytia joTinstoni (fig. 56). These annulations are sometimes spirally 

 arranged as ia Cam/panularia spiralis (fig. 59). Some of these annulated gonangia remind one 

 quite forcibly of Chinese lanterns in their general form. 



Extracapsular sporosacs are found in a few forms of Campanularidse, as in Orthopyxis 

 everta (fig. 50). In this case the medusa ripens within the gonangium and discharges its contents 

 into a globiilar or bladder-like structure surmounting the oral or mouth end of the gonangium. 

 Certain species of Silicularia have greatly elongated gonangia, e. g., S. rosea and ;S^. divergens 

 (fig. 60), and in this genus the gonangial walls are often greatly thickened to correspond to 

 the remarkably thickened walls of the hydrotheca. 



There are a few strangely modified gonangia in this family, although they are not so highly 

 specialized as in certaua Sertularidse, as in the genus Diphasia. One of the longest known and 

 most remarkable of the strongly modified gonangia is found in the genus Gonothyrsea (fig. 58), 

 where it is a characteristic featm^e. We find here the unique extracapsular medusae to which 

 Alhnan has given the name "Meconidia."^ These appear as sessile medusae resting on the top 

 of the gonangium, there being usually two or three such structures on the top of each gonangium. 

 These meconidia are formed very much as ordinaiy gonophores on the blastostyle within 

 the gonangium, appearing at first as mere hernia-hlce protrusions of the latter and sevferal 

 appearmg in dififerent stages of development on the same blastostyle. The oldest medusa is 

 at the distal end of the blastostyle and is carried out through the end of the gonangium while 

 still restmg on the plug-like end of the blastostyle. 



The meconidia, particularly in female colonies, bear the characteristic structiu-es of 

 medusae, showing radial canals, proboscis, circular canal, and marginal tentacles. The ova 

 are developed into planulae within the meconidia and later escape through the oral end of the 

 latter. In the male colony the medusa characters are more obscure, and large ovoid spermaries 

 are developed, from which escape the spermatozoa in incredible numbers. 



Dm-ing the extracapsular existence of the meconidia their connection with the blastostyle 

 is evident, the tubular cavity of the latter being in direct communication with canal systems 

 of the former. This is the only instance known to the writer in wlfich a sessUe medusa is produced 

 by a calypteroblastic hydroid, although such instances are not uncommon among the gymno- 

 blastic forms. 



Weismann ^ has carefidly worked out the structural and histological details of these 

 remarkable structures, and has graphically represented them in plate 10 of his monumental 

 work. 



A rather unusual form of gonangium is presented by Orthopyxis compressa (fig. 52), in 

 which the veiy stout gonangium is laterally compressed so as to have the form of an elongated 

 ellipse in cross section. Another very pecuhar form is found in Campanularia calceolifera (fig. 51 ), 



' Gymnoblastic Hydroids, 1871, p. 58. 



* Die Enlstehung der Sexualzellen bei den Hydromedusen, 3883, p. 131. 



