31 



en sadflfonuig (InMielthhurc. der altsaa fra forste oieblik 

 omgiver p:ja'lletannen til begge sider og dorsalt. Se fig. 

 8, pl. IX. Fra peribraiichialsækken vokser tidlig forover 

 et blindt endende ror, livis l>agrp munding sees paa iios- 

 staaende tekstfigur. Se forøvrig pl. IX, fig. 6. Dette rør, 

 som det lykkedes mig at forfolge gjennom alle stadier paa 

 længde- og tversnit vokser dernrest sammen med gjælletar- 

 men fortil og det danner saaleile.s en rortormig forbindelse 

 mellem gjælletarmen og iieribrancliialsækken, fig. 7. pl. IX. 



Under den videve udvikling snores nu roret af fra 

 peribrandiialsækken, idet det lukker sig bagtil, og vi finder 

 det da, som af bildet i fig. 8 (ijl.IX) kun staaende i for- 

 bindelse med gjælletarmen fortil. T det følgende vil vi 

 kalde dette rør ..dorsalroret" for ikke at foregribe noget 

 angaaende dets videre skjæbno og betydning. 



Medens nu P/zoii og (}J:a liegge mener, at dorsalroret 

 alene danner hypophysis. fandt jeg, at gangliet afsnorede 

 sig fra dets ventrale side. Eoret var med andre ord at 

 opfatte som et fælles anlæg for liypopliysis og centralnerve- 

 svsteni. t't forhold der forekom mig at faa foroget interesse 

 derved, at det ogsaa hos larverne lykkedes mig at vise» . 

 at disse orgfiner fremgaar fra et fælles rorforniigt anlæg 

 (medullarrøret) om end her udviklingen forlober anderledes 

 og frembyder mere comi)licerede forhold. 



Deriniod lykkedes det mig ikke med sikkerhed at af- 

 gjøre, hvorfra hjertet og pericardiet .anlregges, idet jeg fandt 

 det første anlæg til djsse organer som en liden cellehob 

 beliggende ved knoppens bagre hoire side. 



PIzon beskriver, derimod det forste anlæg som en ud- 

 bugtning af den indre blære (sous forme d'un jjetit diverti- 

 cule inférieur de la vésicule ondoderrairjue primitive.. (48 a, 

 pag. 150). Denne meddelelse stemmer fuldt ud med. hvad 

 vi for Pevoylioras vedkommende meddelte efter Koivalev- 

 ■d-ij. Den lille cellehob bar forst intet distinct himen, 

 siden omdanner den sig til en blære, der saavel indeholder 

 aulægget til hjertet som til ])ericardiura og af denne dan- 

 nes hjertet ved udbugtning. en proces, der er vel kjendt 

 fra rem Bcnrden o// Julius undersogelser. 



Generationsorganerne vandrer eller forskyves fra mo- 

 derdyret nid i knopperne. Det synes efter mine undersø- 

 gelser, som om generationsorganerne udvikler sig mere eller 

 mindre uafhængigt af knoppen, idet jeg snait fandt ganske 

 unge knopanlæg med store ægfoUikler, snart ældre knopper 

 uden eller med ganske smaa ægceller. Æggenes resp. te- 

 stiklernes udvikling antages ogsaa at ftn-tsætte sig gjennem 

 flere generationer, et forhold, der forekommer mig san-deles 

 eiendommeligt, og som jeg ikke vover at give nogen for- 

 klaring for. Ligesaa eiendommelig er det forhold, at de 

 første spor til generationsorganer forst viste sig i den 4de 

 generation fra ægget af. 



Som ovenfor nævnt stemmer denne fremstilling i ho- 

 vedpunkterne overens med Piioiis f)g 01;as arbeider. An- 



mediately as a saddle-shaped double vesick'. wjiieh thus 

 from the very first surrounds the branchial gut on both 

 sides :ind dorsally (See Pl. IX, fig. 8). Forwards from 

 the peribranchial cavity, there early grows a cæcally-ending 

 tube, wliose posterior opening is seen in the abovc text- 

 figure (See also Pl. IX, fig. 6). This tube, whicii I suc- 

 ceeded in following through all tlie stages in longitudinal 

 and transverse sections, thereupon coalesces witli tiie bran- 

 chial gut in front, and tims forms a tubular connection 

 lietween the branchial sac and tiie pei-il)ranchial cavity 

 (Pl. IX, fig. 7). 



During its further development, tlie tube is constricted 

 from the peribrancliial cavity, whiie it doses behind. and 

 we then find it, as figui'ed on Pl. IX, fig. 8, communica- 

 ting only with the branchial sac in front. \\e will call 

 this tube the „dorsal tube", so as not to anticipate any- 

 thing concerning its future destiny and significance. 



While Pkon and 01;a both think tiiat the dorsal 

 tube only forms the hypophysis. I found tiiat the ganglion 

 was constricted from its ventral side. In other words, the 

 tube nmst be considei-ed as a common rudiment of the 

 hypophysis and the central organs of the nervous system, 

 a circumstance which seemed to me to gain fresh interest 

 from the fact that in the larva too, I succeeded in showing 

 that these organs originate in a common tubular rudiment 

 (the medullary tube), although here the cøurse of development 

 is otherwise, and presents more complicated conditions. 



On the other hand, I did not succeed in determining 

 with certainty where the heart and the pericardium origi- 

 nate, as I found the earliest i-udiment of these organs in 

 the form of a little mass of cells situated to the rigiit of 

 the posterior side of tiie bud. 



Pizon. on the other hand, describes the earliest rudi- 

 ment as an evagination of the inner vesicle (sous forme 

 dun petit diverticule inférieur de la vésicule endodermique 

 l)riniitive", 48 a, p. 150). This statement agrees perfectly 

 with what we recorded from Koicalcrslnj, as regards Pero- 

 pliiDii. The little mass of cells has at first no distinct hi- 

 men; it is subsequently converted info a vesicle, which 

 contains the rudiments of both the heart aud the pericar- 

 dium, and from whicli the heart is formed by evagination, 

 a process that is wi'll kmiwn from ran Benedeii and Jid/n's 

 investigations. 



The generative organs waudor, or are displaced from 

 the pareiit animal iiito tiie I)uds. From my investigations, 

 it seenis to me tiiat the generative organs develope more 

 or less independently of the bud, for I sometimes found 

 quite youiig, rudimentary buds with large egg-follicles, at 

 otliers, older buds without any, or with only very small 

 egg-cells. The development of the eggs, as of the testicles, 

 is also probably continued through several generations, a 

 fact which seems to me most peculiar, and of which 1 will 

 not venture to give any explanation. Equally peculiar is 

 the circumstance that the first trace of generative organs 

 appcared in the fourtli generation from tiie egg. 



As mentioned above. this account agrees in the main 

 witli Pizons and (>ha's works. With regard to certaiii 



