103 



Folere o,o' delvis ogsaa Mandibulurfodderne, hvorved 

 snart Kyg- snart Bugside vendes opad. 



Et noget senere Stadium er tremstillet Fig. 3 

 fra Bugsiden. Larven har nu naaet en Længde af 

 0,47 mm og har Tjegemets bagre Afsnit end niere 

 ibrlænget, skjondt fremdeles uden Spor af Lemmer. 

 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 Lidsnit, 

 i hvis Bund Analaabningen er beliggende. 1 det 

 indre af Overlæben sees flere meget tydelige celle- 

 agtige Legemer, aabenbart af kjertelagtig Natur, og 

 dens terminale Fortsats er nu fuldkommen saa lang 

 som den proximale Del af Overlæben og skraat 

 nedadrettet. Mandiliularfoddernes Rodstykke har 

 sondret sig skar])ere fra Legemet og forlænget sig 

 indad mod Mnndaabningen, hvorved det nu meget 

 tydeligt viser sig at repræsentere Kindbakkernes 

 Corpus. 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 

 Lidhold fyhlte Tarmkanal med stor Tydeliglied 

 skinner igjennem de tynde Integumenter. 



Fig. 4 fremstiller (fra Rygsiden) et betydelig 

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

 ven har nu en Længde af Ofib mm. og har under- 

 gaaet flere væsentlige Forandringer. 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 forste S|)or af de sammen- 

 satte Øine i Form af 2 smaa, endnu vidt ailskilte 

 Pigmentpletter, dor ligger til hver Side og noget 

 ovenfor det enkle Oie. Jjereb(nillet har ment, at de 

 sammensatte t)ine dannedes ved en Afspaltning fra 

 det enkle Øie, hvad der er aldeh's urigtigt. De 

 dannes ganske uafhængigt af det enkle Oie, der 

 baade hvad Storrelse og Form angaar, er fuldkom- 

 men 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 Bugsiden. Paa 2det Par har <1(mi basale 

 Fortsats klovet sig i Enden i 2 borsteformige, tæt 

 eilierede Spidser, og den bagre Gren har faaet en 

 Svommeborste flere paa Spidsen. Mandibularfodderne 

 viser nu alle sine 3 Led meget tydeligt begra'ndsede, 

 og den fra næstsidste Led udgaaende Borste har 



than behind. The larva, which is now 0.3tj mm. in 

 length, swims about with tolerable ra])idity in the 

 water, with rhythmical strokes of the 2nd pair 

 of antennas and partly of the mandibular legs, 

 whereby now the dorsal, now- the ventral surface is 

 turned uppermost. 



A somewhat later stage is represented in tig. 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 limlis. The terminal ])ro- 

 jections, whieli evidently answer to the caudal claws 

 in the adult animal, have increased considerabh- in 

 length, and are se])arated from each other by a 

 deep emargination. at the bottom of which the anal 

 aperture is situated Inside the labrum are visible 

 several very distinct cellular bcjdies, evidentlv of a 

 glandular nature; and its terminal projection is 

 now fully as hiug as the proximal pai't of the 

 labrum, and directed obliqiiely downwards. The 

 liasal ])art of the mandibulai- legs has become moi-e 

 sharply divided from the body, and is produced 

 inwards towards the oral aperture, thereb\- showing 

 very clearly that it represents the bodj^ of the 

 mandibles. The limbs themselves, however, do not 

 seem to have undergone any essential change in 

 their structure. The body in this stage is consider- 

 abl}^ more transparent than in the two preceding- 

 stages, being almo.st as clear as water, so that the 

 intestinal canal, with 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. The 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 ]iosterior section, not including the 

 terminal projections, is twice as long as the ante- 

 rior, from wliich it is separated by a very distinct 

 contraction, inside the head, the earliest traces of 

 the compound (n'cs now appear in the shape of two 

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

 lying one on each side, and somewhat above the 

 ocellus, iierebouliet thought that the com])ound 

 eyes were formed by a splitting ofl' from the 

 ocellus, a theory which is altogether incorrect. 

 They are formed i[uite independently of tlie ocellus, 

 which, both as regards size and shajie, 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 jirojec- 

 tion has divided at the end into 2 bristle-like, thickly 

 ciliated points, and the posterior ramus has acfjuired 

 another natatory liristle at the point. The man- 

 dibular leers now show all their 3 joints very 



