tory of the species was orip;inally undei'takon and has since 

 boen prosecuted with Dr. Murbach's kind encouragement, and 

 I have received from him many favors in the way of material 

 and helpful suggestions. The work has been carried on dur- 

 ing the past two years at the U.S. Fish Commission laborato- 

 ry, whei-e I have had the great privilege of working during 

 the summer, and under the direction of Professor W. K, 

 Brooks at the Biological Laboratory of the Johns Hopkins 

 University, I wish to acknowledge my obligations to T)r, 

 Bumpus , Dr. II, K, Smith and Dr. V/hitman for courtesies 

 which they have extended to me in my work. 



Note on the Ontogeny of the Trachomedusae . 



Gonionema . according to Ilaeckel's classification, falls in- 

 to his third order, the "Trachomedusae". Haeckel character- 

 ized this order as follows: "development, hypogenesia 

 (not metagenesis), but usually with metamorphosis". Subse- 

 quent research into the life-history of members of this 

 group has shown that each clause of this statement is open 

 to emendation. In the first place, the "usually" is super- 

 fluous, and therefore ei-roneous. The exceptions which 

 Haeckel supposed to exist and which caused him to say "usu- 

 ally with metamorphosis" have been shown to be no excep- 



