176 INTRODUCTION. 



I have studied the extensive collection in the Museum of Comparative 

 Zoology, rich in West Indian material, and also the collections of the U. S. 

 National Museum, including a valuable series of Velella and Physalia from the 

 Pacific. 



With such a wealth of material the time seemed ripe for a more adequate 

 presentation of oui- knowledge of the group than would be associated with the 

 mere description of the "Albatross" specimens. Haeckel's monograph, loaded 

 down as it is with no less than twenty-three nomena nuda of his own making, 

 and with many new species, beautifull.y figured, but none of them critically 

 studied from the systematic standpoint, can not be used as a manual of the 

 group. The list of Atlantic species given by Chun in his report of the col- 

 lections made by the "Plankton" Expedition, is a great advance; but this 

 takes no account of the Indo-Pacific species, and, besides, during the last twelve 

 years our knowledge of the group has grown along many lines. A revision 

 has been attempted by Schneider; but the reductions which he proposed are 

 so sweeping and in many cases so unnatural, that they have not been generally 

 adopted. 



I have sought less for a well-balanced scheme of classification, than to 

 present the actual state of our knowledge. The lacunae are still far too great 

 to allow a systematic revision of the group in the sense in which such is possible 

 for birds, or for mammals. By emphasizing these gaps, other researches may 

 be stimulated, and thus the desirable end be obtained. 



Among Siphonophores we constantly encounter doubtful species, which 

 inay or may not be distinct from their nearest allies. To justifj' their union 

 with other forms we must have something more than a fair probability. Other- 

 wise we are likeh^ to mask existing and important differences. In several 

 such cases I have been able to base vuiions on the actual comparison of speci- 

 mens of the forms concerned, and whenever unable to do this, it is so noted. 



In cases where direct comparisons have not been made, and where the 

 published descriptions are not conclusive, it is better to allow both species to 

 stand. 



The nomenclature of the Siphonophores has long been a bete noire. The 

 labors of Bedot and of Chun, have brought some improvement, but there is 

 still much confusion. In such a group as the present, uniformity can only 

 be hoped for through a strict application of the law of priority; and especially 

 must we follow the rule of applying to a species as a whole the name first applied 

 to any part of it or its larva. ' But what should be done with the older names 



