No. 11. — Studies from the Newiport Marine Zoological Laboratory. 

 Communicated hj Alexander Agassiz. 



XV. 



On the Development of Agalma. By J. Walter Fewkes. 



The genus Agalma, in its growth from an egg into the adult, passes 

 through three larval stages which can be readily distinguished from each 

 other. These larvse, from the nature of the growth of the Agalma colony, 

 are not separated from one another by clearly marked distinctions, but 

 temporary organs found in one stage are often carried over to the next 

 in the course of the passage of one larva into that next following. The 

 peculiaritie'^, however, of each are strongly enough defined to justify the 

 division of the embryological history of Agalma into the three stages to 

 which reference is made. 



These three characteristic larvce about which the young of the genus 

 Agalma group themselves have been given the following names : 1. The 

 primitive larva ; 2. The Athorybia stage ; 3. The larva like the adult 

 in general features, altliough possessing together with organs of the 

 adult certain provisional structures bequeathed to it from the earlier 

 conditions of growth through which it has passed. 



The last two of these larval stages are not considered in this paper, 

 except incidentally to record observations on certain appendages of the 

 Athorybia stage, showing the fate of organs of permanent and others of 

 provisional nature which play an important part in the appearance ot 

 the youngest or primitive larval condition. The present contribution 

 deals with the outward changes in the growth of the egg from fertiliza- 

 tion to the primitive larva. In that epoch many important organs, some 

 of which persist into the adult, originate ; and, more significant still, at 

 that time first arise the three layers out of which every organ of the 

 whole colony is developed. The development of the first of the three 

 larval stages of Agalma may consequently be looked upon as a key to 

 the phylogeny of the Oceanic Hydrozoa. It is therefore at all events 

 necessary, before we can trace the relationships of different genera widely 



VOL. XI. NO. 11. 



