2 AMEBICAN HYDROIDS. 



that has elapsed since the pubUcatioii of Agassiz's monumental work. Nothing at all com- 

 parable with this work has been produced by any subsequent American writer on the Campan- 

 ularidis, considered from the standpoint of the colonial fixed forms rather than from that of 

 the medusae. 



Alexander Agassiz/ in his "North American Acalephse," adds but Uttle to our knowledge 

 of the morphology of this group, and most of the work done by subsequent writers in this country 

 has been in the way of faunal lists and systematic discussions. An excejition to this statement 

 should, however, be made in the case of Dr. A. G. Mayer's beautiful monograph of the Medusas 

 of the World,^ in which are a number of excellent descriptions and figures of medusa of Ameri- 

 can hydroids belonging to the Campanularidse, although that author places them in the family 

 "Eucopiidaj," which contains several medusas whose hydroidj forms would not go into the 

 Campanularidse as used in this work. A number of beautifully colored figures, both of medusae 

 and hydroid forms, are found in this work. 



Many important treatises on the morphology of the Hydroida, including descriptions 

 of species now known to occur in American waters, have been produced by European naturaUsts. 

 Among the earher writers to discuss morphological details was P. J. van Beneden,'' who pub- 

 lished some excellent descriptions and drawings giving details of structure of both trophosome 

 and gonosome, including free medusee, of several well known campanularians. He seems to 

 have been among the first to clearly demonstrate the connection between the medusae and 

 hydroid colonies of this group. 



The earliest recognition of this connection that I have found, however, is given by Johnston,* 

 who describes how Mr. Peach, in 1842, demonstrated the connection between the medusae and 

 colonial forms of Ohelia dichotoma and of a Campanularia which appears to have been Olytia 

 johnstoni. 



While Hincks ^ gives an excellent general account of the gross morphology of the Campanu- 

 laridae, the first comprehensive and detailed description must be accredited to Alhnan," who 

 discusses many points of interest concerning the Campanularidas, including the true nature of 

 the sex buds of the medusae of Olytia johnstoni, the homology of the medusa and hydranth, 

 details of the gonangia and gonophores of several species of Campanularia, Ohelia, and Gono- 

 ihyrasa, the development of ova and spermatozoa in Oampanularia Jlexuosa, the development 

 of the hydranth and blastostyle in the same species, a masterly description of alternation of 

 generation, and a study of the hthocysts of Olytia johnstoni and Ohelia geniculata. 



Haeckel's splendid monograph "Des Systemes derMedusen," 1880, contains brief descrip- 

 tions of a few medusae belonging to the genus Ohelia, and descriptions and figures of Eucope 

 campanulata and Olytia johnstoni. 



Thallwitz^ worked out with great care the origin of the spermatozoa in Oampanularia 

 jlezuosa, and Weismann * describes and figures the origin of the ova in Gonothyrsea loveni. 



TROPHOSOME. 



The colonies of the Campanularidse are, in general, more simple than in the families pre- 

 viously described. Wliile occasional specimens are found attaining a height of a foot or more,° 

 the colonies are usually small and inconspicuous. 



' Illustrated Catalogue of the Museum of Comparative Zoology, No. 2, 1865. 



2 Volumes 1 and 2, 1910. 



' M^moire sur les Campanulaires de la Cote d'Ostend, 1845. 



^Hist. Brit. Hydroid Zoopli., ed. 2, vol. 1, 1847, p. 119. 



^ British Hydroid Zoophytes, 1868. 



^ Gymnoblastic Hydroids, part 1, 1871. 



' Ueber die Entstehung der mannlichen KeimzeUen bei deu Hydroiden, Jenaische Zeitschrift, vol. 18, 1885, 

 p. 390, pi. 12. 



" Die Entstehmig der Sexualzellen bei den Hydromedusen, 1883, pi. 10, and explanation. 



" Agassiz describes colonies of Laorriedea (=Ohdia gelatinosa) that were found growing to a height of 15 to 20 inches 

 in the brackish waters of the Charles River near Boston. 



