37 



Af den givne fremstilling af knopskydningeii vil man 

 forståa, at ét iudividiuni fuar to tarnitrakti. naar kun ab- 

 dorainalknoppen dannes (teksfigur 11); ligeledes at to thora- 

 caldele anlægges. naar alene thoraeaUauippen kommer til 

 ndvikling. 



Hjertet og perikardiet dannes efter CauUery fra en 

 udbngtning af epikardiets distale ende. 



Yed disse Caulleri/s udmerkede undersogelser er ogsaa 

 denne familie l>ragt i overensstemmelse med de andre. 



Poiycliniderne. 



I sin grundlæggende af handling: ..Ueber die Knospnng 

 der Ascidien- har Koiralevski/ ogsaa behandlet Foh/cJini- 

 denie, idet han studerede Aiiiaruiiiiuiii iirolijei-tim. Som 

 iiævnt i kap. 2 dannes knopperne derved, at moderdvrets 

 postabdomen paatvers deles i 4 a 5 dele, der hver ndvikler 

 sig til en knop. (Se pl. X, fig. 7 og 8). Knopanlæggets 

 indre blære frenigaar da nmiddelbart af postabdomens 

 ,.skillevæg", der som vi .saa i kap. 1 er en fortsrettelse af 

 epikardiet. Det Ivkkedes mig at bekræfte dette punkt, idet 

 jeg forst iios lai-verne af Amaroucium roseum fandt anlæg- 

 get til epicardiet som en liden dobbelt udbugtning af tarm- 

 traktus"æsophagealparti (fig. 6, pl. X), dernæst hos indi- 

 vider, der havde gjennemgaaet larvernes metamorphose 

 fandt epicardiet som et langt ror. der distalt stottede sig 

 til pericardiet og centralt indmundede i tarmtraktus ved 

 Y-formige forgreninger paa den bekjendte forst af van Be- 

 tieilen og Jul/n beskrevne maade (se pl. X, fig. 9). Idet 

 nu epicardiet sterkt forlænges og herunder skyver hjertet 

 med dets pericardium ud i en hududbngtning dannes post- 

 alidomen. som vi finder den beskrevet af KoiralrrsJnj (fig. 

 7, pl. X), hvor epicardiet sees i postabdomens midte som 

 et ganske fint ror. Det vil herved være Ijevist, at knop- 

 jaernes indre blære dannes fra moderdvrets epicardium og 

 at -dette er en cntodermal dannelse (se pl. X, fig. 8). 

 Koiralevslys videre beskrivelse af knopskydningens forlob 

 stemmer nu i hoi grad overens med det tidligere for andre 

 grupper meddelte skema, om den end i flere detailler af- 

 viger fra de senere undersogelser af Pizoii (48 «), forfatte- 

 ren (31) og CanlJeiij (9). I det folgende skal jeg forst 

 meddele knoi)skydningens forlob efter mine egne undersøgel- 

 ser og skal jeg deretter omtale de forskjellige afvigelser. 



Fig. 1. pl. XI og fig. 10. pl. X giver et billede af 

 et ungt stadium, der giver os en forklaring over alle de 

 forste udviklingsprocesser. Man sev, at den ydre blære 

 ligesom hos de andre grupper ikke deltager i organernes 

 dannelse. Den indre blære undergaar imidlertid flere sam- 

 tidigt foldeprocesser. Paa hoire og venstre side bugtes de 

 2 anlæg til dannelsen af peribranchialsækken ud. Hvad 

 der imidlertid her er eiendommeligt er at dorsalrøret bugtes 

 ud sammen med venstre peribranchialsækanlæg (se pl. X, 



From the abovo description of this budding, it will 

 be understood tliat one animal has two intestines when 

 only the abdominal i)ud is formed (text-figure 11); also 

 tliat two thoracic parts commence to form when only the 

 the thoracic bud is developed. 



The heart and pericardium are formed according to 

 CaiiUcr// from an evagination of the distal end of the epi- 

 cardium. 



By these i-emarkably good investigations o( CaiiUefys. 

 this family also is Ijrought into harmonv with the othei-s. 



Polyclinidæ. 



In his fundamental treatise ..Uelx-r die Knospung 

 der Ascidien-, Koinderski/ has also treated of the Poli/- 

 cliuidæ. iiaving studied Amaroiiciuni prolifennii. As stated 

 i n Chapter II, the buds are foi-nied by a transverse division 

 of the post-abdomen of the parent animal into 4 or .") 

 parts, each of which developes into a bud (se Pl. X, figs. 

 7 and 8). The inner vesicle of the rudimentary bud arises 

 immediately from the septum of the post-abdomen, which. 

 as \ve saw in Chapter I, is a continuation ot the epicardium. 

 I succeeded in confirming the accuracy of this point, having 

 first in larvæ of Amaroiididii roseum found the rudiment of 

 the epicardium as a little double evagination of the æso- 

 phageal part of the intestine (Pl. X, fig. 6), and then in 

 animals that had nndergonc the larval metamorphosis, I 

 found the epicardium as a long tube wliich rested against 

 the pericardium distally, and ceutrally opened into the ali- 

 inentary canal by Y-shaped ramifications in tlie well-known 

 manner first described by van Beneden and Jidin (see Pl. 

 X, fig. 9). With the great increase in lengtii of the epi- 

 cardium, whereby the heart and its jjericardium are pushed 

 out into a cuticular evagination, the post-abdomen is formed 

 as \ve find it described by Ko!valevsJ:y (Pl. X. fig. 7j, 

 where the epicardium is visible in the middle of the post- 

 abdomen as a very thin tube. This will serve to prove 

 that the inner vesicle of the bud is formed from the epi- 

 cardium of the parent-animal, wiiicii is an endodermal for- 

 mation (see Pl. X, fig. 8). KoivalevsJiys further description 

 of the course of budding agrees very exactly with the plan 

 given previously for other groups, although it differs in 

 several details from the more recent investigations of Pi- 

 zon (48 a), the present writer (31) and Caidleiy (9). I 

 will here first describe the course of budding according to 

 my own investigations, and will then mention the various 

 deviations. 



Pl. XI, fig. 1 and Pl. X, fig. 10 illustrate a very 

 eai'ly stage, which afiords us an explanation of all the 

 earliest developmental processes. It will be seen that the 

 outer vesicle. as in the other groujis, does not take part 

 in the formation of the organs. The inner vesicle, how- 

 ever, undergoes several simultaneous folding processes. Ou 

 the right and left sides, the 2 rudiments for the formation 

 of the peribranchial cavity bulge out. The remarkable 

 thins here. however. is that the dorsal tube bulges out 



