Den ber giviie fremstilling stemmer i de vresentligste 

 træk med Kowalevshys ældre grundlæggende undersogelser. 

 Koivdevsky skildrer (35 og 36), hvorledes der, kort efterat 

 neiiroporus har lukket sig, dannes en ny aabning fra nerve- 

 systemet (medullarroret) nd til larvens dorsalside ved en 

 sammenvoksning af ektodermen og hjerneblæren, samt at 

 denne forbindelse mellem lijerneblære og ektodermen lidt 

 efter lidt forskyves ind i gjælletarmen, idet det ektoderm- 

 parti, der staar i sammenhæng med jhjerneblæren bugter 

 sig ind og danner larvens ingestionsaabning (,.fortarm", 

 stomodæum). „Da nun die Oeffnung des eingestiilpten 

 Theiles zum Munde wird, so bleibt die Mundung der 6e- 

 hirnblase etwas tiefer nnd wird zu der bekannten Flimmer- 

 scheibe, von welcher aus die flimmei-nde Banchrinne be- 

 ginnt" (pag. 118, 36). Det blivende ganglions og hypophy- 

 sens dannelse blev ikke behandlet af Kowahvskij, hvilket 

 vil forstaaes deraf, at han kun beskrev æggets udvikling 

 indtil larvestadiet og ikke metamorphosen. 



Hypophysens dannelse blev nu af van Beneden og 

 Jidiii (2) samt Seeliger (58) skildret som helt uafhængig 

 af medullarroret, idet disse forfattere opfattede hypo- 

 physen som en udbugtning af gjælletarmen (entodermen). 

 Især har van Beneden og .Tidin indgaaende skildret dette. 



Imidlertid havde tiere forfattere allerede tidligere be- 

 skrevet en forbindelse mellem larvehjernen og gjælletarmen 

 gjennem flimmergruben, saaledes hos Åscidierne Lahille 

 (■41), Maurice (-13), Frk. Sheldon (63) og hos salperne 

 Sdlenshj og Metvalf. 



VæsentHg for at vinde støttepunkter for en sammen- 

 ligning mellem knopper og larver undersogte Widey (65 og 

 67) og forfatteren (31) samtidig sporgsmaalet hos forskjel- 

 lige famiher af Åscidierne, og kom herunder til identiske 

 resultater i overensstemmelse med den ovenfor givne frem- 

 stilling. 



I modsætning hertil lieskriver Fhon (48 a og h), at 

 der fra larvens entoderm dorsalt bugtes ud et i'Or, der bag- 

 fra vokser i retning forover hen til larvehjernen og ninnder 

 ud i dennes sandseblære. Paa et senere stadium skal saa 

 dette rør vokse videre forover fra larvehjernen og frem til 

 stomodæum og saaledes i sit forreste parti danne flimmer- 

 gruben. Under den senere udvikling skal forbindelsen med 

 larvehjernen igjen løses, og røret fremstiller da hypophysen, 

 idet dets bagre ende loser sig fra d-en oprindelige forbin- 

 delse med gjælletarmen. (Dette forhold paralleliserer Pizon 

 med sin beskrivelse af hypophysens dannelse hos knopperne). 



Det blivende ganglion dannes ogsaa efter Fizon fra 

 hjerneblæren. 



Den af Wdley og forfatteren givne beskrivelse er 

 senere bekræftet af SaJensky (55), der har tilfoiet en ind- 

 gaaende beskrivelse af larvehjernens bygning, af v. Kupfer 

 (40), der ligesom forf. beskrev Disfaplia inagnilarva, samt 

 af Caudenj (9), der undersøgte Circinalium concrescens, Di- 



The deseription here given agrees in its prineijial 

 features vdthKoiualevskg^.i: older, fundamental investigations. 

 Koivalevsky describes (35 and 36) bow, shortly after the 

 neuropore closes, a new opening is formed from the nervous 

 system (meduUary canal) out to the dorsal side of the 

 larva by a syraphysis of the ectoderm and the cerebral 

 vesicle, and that tiiis communication between the cerebral 

 vesicle and the ectoderm is gradually intruded into the 

 branchial gut, tiiat part of the ectoderm which is in con- 

 nection with the cerebral vesicle being invaginated and 

 forming the arva's oral aperture (fore-intestine, stomodæum). 

 ..Da nun die Oeffnung des eingestiilpten Theiles zum Mund 

 wird, so bleibt die Mundung der Gehirnblase etwas tiefer, 

 und wird zu der bekannten Flimmerscheibe, von welcher 

 aus die flimmernde Banchrinne beginnt-' (36, p. 118). The 

 formation of the permanent ganglion and hypophysis was 

 not touched upon by Koivalevsky, a circumstance wliich is 

 explained by the fact that he only described the develop- 

 ment of the ovum as far as the larva stage, and not to 

 the metamorphosis. 



The formation of the hypophysis was now described 

 by van Beneden and Jnlin (2) and by Seeliger (58) as 

 totally independent of the raeduUary tube, these writers 

 having regarded the h}q)ophysis as an evagination of the 

 branchial gut (the endoderm). Van Beneden and Julin 

 in particular, iiave descrit)ed this in detail. 



Several authors iiad, however, already described a 

 communication between the larval brain and the branchial 

 gut, through the dorsal tubercle, viz. Lahille (41) Maurice 

 (43) and Miss Sheldon (63) in the Ascidiæ, and Salensky 

 and Metccdf in the Saljyce. 



Chiefly witli a view to galning points of support for 

 a comparison between buds and larvæ, Willey (65 and 67) 

 and the present wnter (31) investigated the question si- 

 multaneously, in various families of Ascidiæ, and thereby 

 arrived at the same conclusions agreeing with the above 

 deseription. 



In opposition to this, Fizon, (48 a and h) states that 

 a tube bulges out dorsally from the larvas endoderm, 

 growing from the back forwards to the larval brain, and 

 opening into the latter's sensory vesicle. In a later stage, 

 this tube is said to grow farther forwards from the larval 

 brain, and on to the stomodæum, tims forming, in its an- 

 terior pai't, the dorsal tubercle. During subsequent deve- 

 lopment, the communication with the larval brain is again 

 broken off. and the tube then represents the hypophysis, 

 its hind extremity having had its original connection with 

 the branchial gut severed. (Fizon compares this witli his 

 account of the formation of the hypophysis in the budj. 



According to Fizon. the permanent ganglion is also 

 formed from the cerebral vesicle. 



The account given by Willey and the present writer 

 was subsequently confirmed by Salensky (55), who has ad- 

 ded a detailed deseription of the structure of the larval 

 brain; by r. Kiipffer (40), who, as well as the present 

 writer, described Distaplia magniktrva; and by Cnidlery 



