94 INTRODUCTORY OBSERVATIONS. 



Stockton-on-Tees," which appeared in 1827. This list still con- 

 tinues to be our chief authority for the zoophytes of that locality, 

 and contains one or two species that have not been found further 

 north. The principal contribution towards a knowledge of the 

 zoophytes of our coast, however, is " A DescrijDtive Catalogue 

 of the Zoophytes of North Durham," by Dr. Johnston, published 

 in the Transactions of the Newcastle Natural History Society, 

 in 1832, and accompanied by plates from the etchings of his 

 accomplished lady. This Catalogue contains much original in- 

 formation; yet, though only twenty-four years have elapsed 

 since its publication, it is interesting to observe how great a 

 change this branch of natural history has undergone during the 

 period; much of which has been effected by the distinguished 

 author himself. The classification there adopted has become 

 obsolete, and even the number of sj)ecies recorded, which Dr. 

 Johnston felt assured at the time would "be found by the Na- 

 tural History Society of Northumberland to contain such a full 

 list of their zoophytes as will suffice to convey an accurate view 

 of their number and variety," has been more than trebled by 

 subsequent researches. A list of the Hydroid species, collected 

 by Miss Ellen Forster, at Tynemouth, in 1839, Vxdll be found in 

 the second edition of " British Zoophytes," and the habitats of 

 others got on the coast are incidentally noticed in the same work. 

 The curious researches of Sars, Daly ell, and other recent 

 authors, leave no doubt of the intimate connexion subsisting 

 between the Hydi-oid species of Anthozoa and the Acalepha ; so 

 intimate, indeed, that in many instances, individuals of the one 

 class can only be considered as immature or transition states of 

 the other. The union between the two classes would conse- 

 qently appear to be inevitable ; but, if we except a few isolated 

 cases, too little is yet known of their embryology and metamor- 

 phoses to allow of any classification in accordance with such a 

 view of their affinities. For the present, at least, they must 

 necessarily be treated of apart. A difference of opinion still 

 exists among naturalists, in cases where a species alternately 

 assumes the characters of each class, as to which should be con- 

 sidered the perfect or typical form. With respect to the Medusae 



