97 



stærk Forstørrelse og da som korte, fine Linier eller Punkter; 

 andre havde næsten antaget Spindelformen, vare svagt 

 turnede og naaede indtil 0.080""" i Længde os 0.008""" i 

 Bredde, Tab. XII, Fig. 63. 64. De optraadte saa tidligt, at 

 kun Ectoderm- og Endodermlagel var dannet med den 

 disse Lag skarpt adskillende Fundamentalmembran. Spik- 

 lerne laa aabenbart i Ectodermlaget, imellem dettes Celler 

 og ligesom afsondret af dem. Alt ettersom Embryonet 

 vuxede. antog del tørst Pæreformen. Cilierne vare længere 

 i den brede Ende, ligesom Spiklerne vare større, tiltagne i 

 Mængde og viste sig mere udprægede som tornede og 

 bladede Spindler, Tab. XII. Fig. 68 — 71; senere under 

 Væxten havde Embryonet bøiet sig indeni Ægget og rik 

 Formen at' en Halvmaane, Tab. XII, Fig. 65; toges det ud 

 at Æggebylsteret, havde det i sit Ydre overmaade megen 

 Lighed med en ungPlanarie, Tab. XII, Fig. 66; Spiklerne 

 laa nu tættere og havde antaget tiere Former, saaledes for- 

 uden Spindelens, timeglas- og korsdannede Firlingers, Fig. 67. 

 Men jo mere Embryonet havde voxet i Længden, jo mere 

 bøiet var det, Tab. XII, Fig. 69, saa at det tilsidst dannede 

 et indeni Ægget sammentrykt S. Tal). XIII, Fig. 43. 44. 

 Spiklerne havde tiltaget noget i Størrelse, saa at ile naaede 

 en Længde af 0.095""", laa tæt sammen, havde mere udpræ- 

 gede Former, Tab. XII, Fig. 72, og ved Tversnit viste det 

 sig, at enkelte Spikler laa nedsænkede i den at' Ectodermet 

 afsondrede, gelatinøse Masse, Tab. XIII, Fig. 39, b. For- 

 uden de nævnte Spikelformer saaes ogsaa enkelte meget 

 smaa Dobbeltstjerner og Koller, samt begyndende sammen- 

 satte Stjerner, Tab. XII, Fig, 72. a. b. c. Det vikle blive 

 for vidtløftigt at beskrive liver enkelt Spikelform hos disse 

 Embryoner, hvorfor jei;- maa henvise til Tegningerne. De 

 hei- omtalte Spikelformer gjælde væsentligt for Nephthya 

 rosea; hos den anden Art, Nephthya polaris, viste Spiklerne 

 sig saa forskjellige, at jeg paa dem let kunde skjelne et 

 Embryo af denne fra et af Neph. rosea, og det samme var Til- 

 fældet med den tredie Art. Spiklerne hos Embryonet af Neph 

 polaris varierede ikke saa stærkt i Former; de van.' ikke 

 >aa stærkt tornede, men mere vingeformede, og Firlinger 

 manglede ganske, Tab. XIII, Fig. 45. Jeg havde til Sam- 

 menligning Embryoner fra begge Arter, hvilke havde op- 

 naaet det samme Udviklingstrin og havde samme Form, 

 men paa Spiklerne kunde jeg allerede paa dette Stadium, 

 medens de endnu laa i Ægget, bestemme Arten. Paa de 

 stærkt sammenbøiede Embryoner saaes altid i den brede 

 Ende en oval Aabning, omgiven at lange Cilier, og som 

 lorte ned til en aflang Hulhed, Tab. XIII, Fig. 43. 44, 

 hvori ved Tversnit viste sig etstorkornetlndhold (Blommekorn). 



Paa et Embryo, der havde forladt Ægget, men op- 

 lml.lt sig i Mavebulheden og var næsten ganske udstrakt, 

 havde Larvemunden en trekantet Form med temmelig 

 brede Læber, Tab. XII, Fig- 70. Om hvorledes det gaar disse 



Den norske Nordhavsexpedition. 1>. O. Danielssen: Akyonida. 



very small that they could with difficulty be measured, and 

 were only visible on powerful rnagnification, and then tbey 

 appeared as minute lines or points; others had almost as- 

 sunied the fusi-form, and were faintly aculeated, and attained 

 np to 0.080»"" in length. and 0.008""" in breadth (Pl. XII. 

 lig- 63. 64). They appeared so early that only the ecto- 

 derm- and the endoderm layers were formod, along with the 

 fundamental membrane which so sharply divides these layers. 

 The spieules lav diselosed in the ectoderm laver, between 

 its cells and as if excreted from them. As the embryon 

 advanced in growtb it first assumed the piriform. The 

 ciliæ were longer in the broad extremity, whilst, also, the 

 spieules were larger and increased in munber, and they 

 showed themselves more distinetly as aculeated and foliated 

 fusees (Pl. XII, figs. 68. 71). Subsequently, during its 

 growth, the embryon had eurved itself inside the ovum and 

 tåken the form of a crescent (Pl. XII. fig. 65). When re- 

 moved from the ovum-covering it had. in its external 

 appearance, very great resemblance to a young Plan/trin 

 (fig. 66). The spieules, now, lay closer, and had assumed 

 several forms, such as, besides the fusiform, also. hourglass, 

 and cruciform quadruplets (Pl. XII, fig. 67). But. the more 

 the embryon had increased in length, the more eurved was it 

 (Pl. XII, rig. (39), so that it, eventually, formed, inside the 

 ovum, a compressed S (Pl. XIII, fig. 43. 44). The spieules 

 had increased, somewhat, in size, so that they attained a 

 length of 0.095""", lay close in to each other and had more 

 clearly defined forms (Pl. XII. fig. 72), and on transversal 

 section it was seen that a irw spieules lay embedded in 

 the gelatinens substance excreted from the ectoderm (Pl. XIII 

 fig. 39, b). Besides the spicular forms named, there were, 

 also, seen, a few very small bistellates and subclavates, 

 also rudimentary complex stellates (Pl. XII, fig. 72, a. b. c.) 

 It would be too prolix to describe, here, each individual 

 form of spicule in these embryons, and 1 must, tberefore, 

 refer the reader to the illustrations. The spicular forms 

 spoken of, here, refer especially to Nephthya rosea. In the 

 other species, Nephthya polaris, the spieules showed them- 

 selves so different that, in it, I was able to distinguish, easily. 

 an embryon of it from one of Neph. rosea, and the same 

 with the third species. The spieules of the embryon et' 

 Nephthya polaris did not differ so greatly in tonn. They were 

 mit su strongly aculeated, but were more pennate, and quad- 

 ruplets were quite absent (Pl. XIII, fig. 45). I had, for com- 

 parison, embryons of both the species, which had attained tin.' 

 same stage of development, and had the same form, but 

 from the spieules I could, even at this stage, whilst they 

 were still in the ovum, determine the species. ln the strongly 

 curved-together embryons there was always seen, at the broad 

 extremity, an oval aperture surmunded by long ciliæ. and 

 which led down to an oblong cavity i Pl. XIII, fig. 43. 44) 

 in which, on transversal section. a coarse granulat' substance 

 i ^ oke-granules) appeared. 



ln an embryon which had abandoned the ovum. but 

 still remained in the ventral cavity, and was almost quite 

 extended, the larva mouth had a triangular form with rather 

 broad Iabiæ (Pl. XII, fig. 70). What happens to these 



13 



