41 



e) Hjertet og pericardiet anlægges hos Botr/jllus som 

 afsnøring af en celleliob af den indre blæres ven- 

 trale parti. Hos Poh/cliniderne dannes organerne 

 fra e})icardiet, de synes altsaa altid i sidste instants 

 at fremgaa at' den indre blære. 



Der foreligger imidlertid flere meddelelser om, 

 at organerne dannes af vandrende mesodermceller, 

 og forfatteren vover ikke at udtale sig bestemt om 

 dette spørgsmaal. 

 /) Ingestions- og egestionsaabningen dannes ved sam- 

 menvoksninger mellem epidermis og den indre blære; 

 gjællespalterne ved lokale sammenvoksninger mellem 

 gjælletarm cg periljranchialsækkens viscerale blad. 

 Karakteristisk er for knopskydningen, at gjælle- 

 spalterne straks anlægges i bestemte rækker. 



4) Generationsorganer og bindevævsceller vandrer, forsky- 

 ves ind fra moderdyret. Musklerne dannes alle af 

 vandrende celler. 



Angaaende generationsorganerne se under Botryl- 

 lidæ. 



fi) The heart and the pericardium commence in Bo- 

 tryllus as a constriction of a mass of cells from 

 the ventral part of the inner vesicle. In PoJi/di- 

 11/(1(1', the organs are formed from tiie epicardiuni, 

 They therefore seem eventually always to originate 

 in the inner vesicle. 



There are however several statements as to 

 the formation of the organs from wandering meso- 

 derra-cells. and the present writer does not venture 

 to give a decided opinion npon tiiis question. 



/) The oral and atrial apertures are formed by the 

 coalescence of tiie epidermis and the inner vesicle ; 

 the branchial stigmata by local coalescences of 

 the branchial sac and the visceral layer of the 

 peribranchial cavity. It is characteristic of budding 

 that the l)ranchial stigmata are in decided rovvs 

 trom the commencement. 

 (4) The generative organs and connective tissue cells wan- 



der, are pnshed in from the parent animal. The mus- 



cles are all formed from wandering cells. 



Concerning tlie generative organs, see under the 



head BotryJlidce. 



Den norske Nordh.avsexpedition. Jolmn Hjort: Kimbladstudier paa grnndlag af Åscidiernes udvikling. 



