I. Distaplia iiiagiii larva. 



Tab. VI. 



I. Distaplia iiiagiiilarva. 



Pl. VI. 



Uuclersogelsen ovev DistapVia nKAf/nilarvas: knopskyd- 

 niug blev i ho.steii I8il4 paal)egyiKlt af Dr. Johan Hjort 

 og mig i fællesskab, og en forelol^ig nieddelel.se om vore 

 resultater offentliggjordes i begyndelsen af 1895 (1). Dr. 

 Hjort har imidlertid senere været for sterkt optaget til at 

 fortsætte dette arbeide, og lian har derfor overdraget til 

 mig den videre udarbeidelse. 



Af DelJa Valles undersøgelser (2), .som senere er be- 

 kræftede af Saleiifl-i/ (3), fremgaar det, at det forste knop- 

 anlæg hos Distaplia magnilarva dannes ved en udl)ugtning 

 af entodermen paa larvens ventrale side og en lignende af 

 ektodermen paa det tilsvarende sted. Begge disse udbugt- 

 ninger afsnores snart ved sin basis, saa at de danner to 

 concentriske blærer, den ydre af ektoderraal, den indre af 

 entodermal oprindelse. Mellem disse blærer tindes spredte 

 mesodermceller, som ved afsnøringen blev skilt fra moder- 

 dyret. 



•Af denne forste knoj) udvikles saa ved delingsproces- 

 ser to eller tre. som alle vandrer nd gjennem larvens celln- 

 losekappe og fuldender sin udvikling nde i kolonien, 



Salenshij har ogsaa leveret en indgaaende fremstilling 

 af de forskjellige organers udvikling hos D/stojJ^/a-knopperne, 

 og efter denne anlægges nervesystemet fra den ydre blære, 

 medens de ovrige onjaner dannes af den indre. 



Dette nervesystemets anlæg fra den ydre likere staar 

 ikke i overensstemmelse med udviklingen hos de dvrige 

 Synascidier, som i de senere aar har været gjenstand for 

 undersogelse. Pi^oiis undersøgelser over Botryllns (4), 

 Hjorts over Botryllus og Polydiiunii (5 og 6), ligesom Caul- 

 leri/'s over Didemnum (7), og Bitters over Goodsiria og 

 sandsynligvis ogsaa FeropJtora (8), viser, at den ydre blære 

 hos disse grupper ingen aktiv del tager i knoppens udvik- 

 ling, men at alle de vigtigste organer dannes ved udbugt- 

 ninger af den indre blære, livad enten denne øjnindelig j 

 skriver sig fra larvens entoderm eller ektoderm. 



Den norske Nurdliuvsexpetlitinn. Kristine Bonnevie: Distaplia magnilarva 



An investigation of the gemmation oi Distaplia magni- 

 larva was beguu in the autumn nf 1894 by Dr. Joluui 

 Hjort and myself, and a prelimiuary record of the results 

 obtained was puljlished in the beginning of 1895 (1). Since 

 then Dr. Hjort has been too much occupied to continue 

 this work, and has therefore entrusted its furtiier disciiarge 

 to me. 



Tt appears from Della Valles investigations (2), whicli 

 were afterwards contirmed l)y Salensl-y (3), that the first 

 indieation of a Inid in Distaplia maynilarra is formed by 

 an evagination of tlie endoderm on tlie ventral side of the 

 larva, and similarly of tlie ectoderm in the corresponding 

 place. Both of these protuberances are soon constricted 

 at their base, so as to form two concentric vesicles, the 

 outer one of ectodermal, the inner one of endodermal origin. 

 Between these vesicles are scattcred mesoderm cells, whicli 

 were separated by the constriction from the mother animal. 



From this tirst bud are then developed by separation 

 processes. two or three more, all of whieh find their way 

 out through the larvas cellulose tunic. and continue their 

 develoiiement out in the colony. 



Saleiisky has also contributed a detailed account of 

 the development of the different organs in the Di^aplia 

 buds, and according to this, the nervous system originates 

 in the outer vesicle, whilc the otlier organs are formed 

 from the inner one. 



This originating of the m^rvous system fioin the outer 

 vesicle does not harmonise witli the development of other 

 Synascidians which have of late years been the subject of 

 investigation. Pizmis investigations on the subject of Bo- 

 tryllas (4), Hjurfs on Botryllus and Polyrlinajii (5 et 6). 

 Caulleri/s on Didemnum (1). aud Bitters on Goodsiria and 

 probably also PeropJtora (8), show that the outer vesicle 

 in these groups takes no active part in the development of 

 the bud. but that all the most important organs are tbrmed 

 by evaginations of the inner vesicle. whether this has its 

 origin in the endoderm or the ectoderm of the larva. 



og Pyrosonia elegans. 1 



