The mesenterial Filaments of the Alcyonaria. 



Edmund B. Wilson, Ph. D. 



With Plates 1 and 2. 



lu studying the developraent of Uenilla I was struck by tbe cu- 

 rious fact tbat tbe so-called dorsal pair of mesenterial filaments appear 

 at different periods iu tbe egg-development and in tbe bud-development. 



In tbe egg-embryo tbey are tbe last to ajipear and develop mucb 

 more slowly tban tbe otber six. In tbe buds, on tbe contrary, tbey are 

 iisually tbe first to appear, and always develop more rapidly tban tbe 

 otbers. 



Since making tbese observations on lieniUa — for a description 

 of wbicb I must refer to my paper in tbe Fbilosopbical Transactions for 

 1883 — I bave made fartbcr observations wbicb lead me to believe 

 that tbis coutrast in develo])ment between the egg-embryo and tbe bud 

 exists in a considerable number of Alcyonaria^ thougb not in all. In 

 the egg-embryos of Leptogorgia virgulata Edw. and Haime, and Cla- 

 ularia ochracea Koch, the development of tbese filaments is quite like 

 'lat of Uenilla. Hence we have representati ves of three leading and 

 vvidely different groups oi Alcyonaria — uamely, foUowing Koch's Clas- 

 sification , tbe Cornularida , Axifera , and Pennatulida — wbicb agree 

 in tbis respect ; and it appears probable that tbis mode of egg-devel- 

 opment is characteristic of tbe entire order. 



On tbe otber band, it is certaiu tbat in tbe bud-development tbe 

 dorsal filaments are the first to appear in many Alcyonaria besides Re^ 

 nilla ; and even wbere tbis is not tbe case, tbey usually develop more 

 rapidly and always attain a greater lengtb tban tbe otber six. For in- 

 stance, Kölliker observed that tbese filaments were fully formed in 

 tbe buds of Halisceptrum at a time wben not a trace of tbe otber six 

 could be made out, and I bave observed tbe same in tbe buds of 



Mittheilungen a. d. Zoolog. Station zu Neapel. Bd. V. 1 



