103 



Følere og delvis ogsaa Mandibularfodderne, hvorved 

 snart Ryg- snart Bngside vendes opad. 



Et noget senere Stadium er fremstillet Fig. 3 

 fra Bugsiden. Larven har nu naaet en Længde af 

 0,47 mm og har Legemets l)agre Afsnit end mere 

 forlænget, skjondt fremdeles uden Spor af Jjemmer. 

 De terminale Fortsatser, som aabenbart svarer til 

 Haleklorne hos det voxne Dyr, har strakt sig be- 

 tydeligt i Længde og er skilt ved et dybt Indsnit, 

 i hvis Bund Analaaluiingen er beliggende. I det 

 indre af Overlæben sees Here meget tydelige celle- 

 agtige Legemer, aabenbart ai kje)'telagtig Natur, og 

 dens terminale Fortsats er nu fuldkommen saa lang 

 som den proximale Del af Overlæben og skraat 

 nedadrettet. jVIandibularfoddernes Rodstykke har 

 sondret sig skarpere fra Legemet og forlænget sig 

 indad mod Mundaabningen, hvorved det nu meget 

 tvdeligt viser sig at repræsentere Kindbakkernes 

 ( 'orpus. Selve Lemmerne synes dog ikke at have 

 undergaaet nogen væsentlige Forandringer i sin 

 Structur. Legemet er i dette Stadium betydelig 

 mere gjennemsigtigt end i de 2 foregaaende Stadier 

 og næsten vandklart, saa at den med gulfarvet 

 Indludd fyldte Tarmkanal med stor Tydelighed 

 skinner itriennem de tvnde Inteijumenter. 



Fig. 4 fremstiller (fra Rygsiden) et betydelig 

 senere Stadium, som er nærved at skifte Hud. Lar- 

 ven har nu en Ijængde af 0,65 mm. og har under- 

 gaaet flere væsentlige Forandi-inger. Legemet er 

 idethele temmelig langstrakt, og det bagre Afsnit, 

 uden at regne de terminale Fortsatser, dobbelt saa 

 langt som det forreste, fra hvilket det er sondret 

 ved en meget tydelig Indknibning. I det indre af 

 Hovedet viser sig nu det første Sjior af de sammen- 

 satte Øine i Form af 2 smaa, endnu vidt adskilte 

 Pigmentpletter, der ligger til hver Side og noget 

 ovenfor det enkle Øie. LerebouUet har ment, at de 

 sammensatte Øine dannedes ved en Afspaltning fra 

 det enkle Øie, hvad der er aldeles urigtigt. De 

 dannes ganske uafhængigt af det enkle Øie, der 

 baade hvad Storrelse og Form angaar, er fuldkom- 

 meu uforandret. Af Lemmerne er Iste Par fuld- 

 kommen af samme Udseende som hos de tidligere 

 Stadier, men synes at være rykkede noget længere 

 ned paa Bug.'iiden. Paa 2det Par har den basale 

 Fortsats klovet sig i Enden i 2 borsteformige, tæt 

 cilierede Spidser, og den bagre (Iren har faaet en 

 Svommeborste flere paa Spidsen. Mandibularfodderne 

 viser nu alle sine 3 Led meget tydeligt begrændsede, 

 og den fra næstsidste Led udgaaende Børste har 



than behind. The larva, which is now 0.36 mm. in 

 length, swims about with tolerable rapidity in the 

 water, with rhythmical strokes of the 2nd pair 

 of antennæ, and partly of the mandibular legs, 

 whereby now the dorsal, now the ventral surface is 

 turned uppermost. 



A somewhat later stage is represented in fig. 3, 

 from the ventral surface. The larva has now 

 attained a length of 0.47 mm and has the posterior 

 section of the body even more elongated, though 

 still without a trace of limbs. The terminal pro- 

 jections, which evidently answer to the caudal claws 

 in tiie adult aninu^l, have increased eonsiderablv in 

 length, and are separated from each other by a 

 deep emargination, at the bottom of which the anal 

 aperture is situated. Inside the lalirum are visible 

 several very distinct cellular 1 indies, evidently (d' a 

 glandular nature; and its terminal projection is 

 now fully as long as the proximal part of the 

 labrum, and direrted oldicpiely downwards. The 

 basal part of the mandibular legs has become more 

 shar])ly divided from the body, and is produced 

 inwards towards the oral aperture, thereby showing- 

 very clearly that it re]iresents the body of the 

 mandibles. The limbs themselves, however, do not 

 seem to iiave undergone any essential change in 

 their structure. Tiie body in this stage is consider- 

 ably more trans]iarent than in the two preceding 

 stages, being almost as clear as water, so that the 

 intestinal canal, Avith its yellow-coloured contents, 

 shows with great distinctness through the thin 

 integuments. 



Fig. 4 represents (from the ventral surface) a 

 very much later stage, when the animal is about 

 to cast its skin. Tiie larva now has a length of 

 0.65 mm., and has undergone several important 

 changes. The body is on the whole rather elon 

 gated, and the posterior section, not including the 

 terminal projections, is twice as long as the ante- 

 rior, from which it is separated by a very distinct 

 contraction. Inside tlie head, the eai'liest traces of 

 the compound eyes now appear in the .sha])e of two 

 small, and as yet widely-separated spots of })igment, 

 Iving one on each side, and somewhat above the 

 ocellus. Lereboullet thought that the compound 

 eves were formed by a splitting off from the 

 ocellus, a theory whicli is altogether incorrect. 

 They are formed (juite independently of the ocellus, 

 which, both as regards size and shape, is altogether 

 unchanged. The 1st pair of limbs is of exactly the 

 same appearance as in the earlier stages, but they 

 seem to have moved a little farther down on the 

 ventral surface. In the 2nd pair, the basal projec- 

 ti(in has divided at the end into 2 bristle-like, thickly 

 ciliated points, and the posterior ramus has aci^uired 

 another natatory bristle at the point. The man- 

 dibular legs now show all their 3 joints very 



