ON DEVELOPMENT ETC. OF THOKONlö. 581 



aquarium ou tlic next morning, I tbuud I liât some younger 

 animais liad attaelied themselves to tlie ti]) or inner-side of the 

 tubes ot" the departed generation ; no doubt they liad been hiding 

 tliemselves somewhere in tlie colonial masses on the previous day. 

 Most of these young worms measured 1-2 cm. in length. 



I bad the same experience in the summer (3f 18*J9. (.)n 

 August '2nd. I visited the place and dived under the ledge of 

 rock where the colonies had formerly Üourisbed ; 1)ut I could ol)- 

 tain nothing Init some decaying masses of the tul)es whicli emitted 

 a disgusting odour. 



Judging from these facts, it seems to me not imj)robal)ie 

 tliat Phovoiiis annually changes its generation. 



As t() the formation of colonies of PhoronU, it may be sup- 

 ])osed that the jiutrescent remains or a certain fluid secreted by 

 the adult act on the larvae as a chemotropic reagent. But this 

 can scarcely be admitted as taking place in the wide and open 

 sea. I think, on the contrary, that this j)he)iomenon is not to l)e 

 attril)uted to such a com])lex cause, l)ut is to l)e regarded merci v 

 as an accidental matter. The colonies of Plwronii^ ijlmai form a 

 compact and rigid mass together with some Ascidians and MoUus- 

 can shells, and adliere veiy tightly to the rocks; so that, when 

 once the animals firm a colony in a suitable ])lace, it mav well 

 be assumed that tliey become gradually luxm-iant. But this is not 

 really the case in .Vl)uratsubo where the colony has remained al- 

 most the same in size for several years. I think, what takes 

 place must be somewhat as follows : the ])laces where the Plioronin 

 colonies are established year after year, nuist naturallv lie well 

 adapted to the life conditions of the worm, and when a large 

 mnnber of larvie is inetamorphosed, as nnist 1)e the case, during 

 the above mentioned months, those larvœ that happen to attach 



