INTRODUCTION. Hit 



based arc, as far as possible, such as may be easily recog- 

 nized. But the generic groups are frequently founded on 

 differences in the reproductive system only; and in such 

 cases it has been necessary to employ the gouozooid as 

 the criterion. For example, Coryne and Syncoryne are 

 identical so far as the trophosome is concerned, and are 

 distinguished solely by the character of the sexual zooids ; 

 in such a case, if the reproductive bodies have not been 

 observed, the only plan is to go through the species of the 

 two genera until we find the description that answers to 

 the form before us. 



An illustration will best indicate the method of employ- 

 ing the Tables. Let Tubularia indivisa be the zoophyte 

 that w r e wish to determine. It has a polypary, but no 

 calycles, and therefore belongs to the Athecate division 

 (Table I.) ; its polypites are associated, not solitary, and 

 therefore under Bracket 1 we are referred to No. 3 for 

 further information. Turning to Bracket 3 we learn that, 

 as it has tentacles of one kind only, we must pass 011 to 

 No. 7. Bracket 7 gives us the choice between capitate 

 and filiform tentacles; and, as our zoophyte has undoubtedly 

 the latter, we are referred to No. 11. There we at once 

 place it under the first division, " tentacles in two separate 

 circles," and are directed to No. 12, where we learn that 

 it is an Ectopleura if it has free gonozooids, and a Tubu- 

 laria if it has not. Should this point be undetermined, 

 we may turn first to the genus Ectopleura, and finding 

 that it contains but a single species, which is minute and 

 not clustered, we shall at once be guided to Tubularia as 

 our goal. 



