. Bulletin of the British Museum (Natural History). EVOLUTIONARY TRENDS IN CAPITATE HYDROIDS AND MEDUSAE 457 COtTMOVHiDAi. HraOC000NI0A£ ArWC7YUDA£ EUDEMDUOAE NrnucriNioAf. ClACOCOftrNIOAC HIBWCHWYIOtf Fig. I. Phylogeny in North American gymnoblastic hydroids as envisaged by Fraser (1943). Kramp in 1949. In it he set forth his views on interrelationships in hydroids of the CorjTnorphidae, the Tubulariidae, Corynidae and related families. He followed Kiihn (1913) in the view that the Corynidae are the most primitive (Text-fig. 2) and from which all other capitate forms are derived. He traced tw
. Bulletin of the British Museum (Natural History). EVOLUTIONARY TRENDS IN CAPITATE HYDROIDS AND MEDUSAE 457 COtTMOVHiDAi. HraOC000NI0A£ ArWC7YUDA£ EUDEMDUOAE NrnucriNioAf. ClACOCOftrNIOAC HIBWCHWYIOtf Fig. I. Phylogeny in North American gymnoblastic hydroids as envisaged by Fraser (1943). Kramp in 1949. In it he set forth his views on interrelationships in hydroids of the CorjTnorphidae, the Tubulariidae, Corynidae and related families. He followed Kiihn (1913) in the view that the Corynidae are the most primitive (Text-fig. 2) and from which all other capitate forms are derived. He traced two separate lines of evolution called the Tiibiilaria-line, and the Corymorpha-line, culminating in the Tubulariidae and Corymorphidae respectively. This theory appeared plausible from the conventional approach, but years of experience on living hydroids and medusae at Plymouth and elsewhere had already inclined me to the belief that the less specialized Corymorphine hydroids were more primitive in all essentials than other capitate forms. The appearance of Dr. Kramp's paper renewed my interest in this question and although I could not accept the view that most of the solitary forms were derived from the colonial Corynidae, it was soon evident to me that any alternative theory on conventional lines would not solve the problem of relationship. This led me to what I am inclined to call basic principles in the classification of hydroids and medusae in order to try to assess the evolutionary significance of the various features on which classifications are based. In attempting to establish basic principles from which to work, I am very conscious that some of them are possibly axiomatic in other fields of zoology and probably by no means new, but in the study of the Hydrozoa there has been remarkably little consideration given to fundamental questions of relating form to function and the probable evolution resulting from it. In this paper it is not possible to present more than an
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