71 



Denne Plade, der er eiendommelig for Slægten 

 Lepidurus, er hos nærværende Art ialmindelighed af 

 forholdsvis ringe Størrelse og som oftest ikke læn- 

 gere end sidste Halesegment er bredt. Formen er 

 mere eller mindre ndpræget tungedannet, nden nogen 

 bemæi'kelig Indsnoring ved Basis. Den varierer for- 

 ovrigt særdeles meget saavel i Størrelse som Form, 

 livad der vil kunne sees af de her givne Figurer 

 (Fig. 23—27), og tiltager ialmindelighed i Længde 

 med Alderen. Fig. 25 fremstiller Halepl aden hos et 

 ganske usædvanlig stort Exemplar. Det er imidler- 

 tid meget sjeldent, at den naar en saa betydelig 

 Størrelse som her angivet. Langs efter Midten har 

 Halepladen hos alle Individer en stiimp Kjol besat 

 med et noget varierende Antal af grove Tagger, 

 sædvanligvis 2 eller 3. Kanterne er i sin ydre Del 

 grovt og noget uregelmæssigt sagtakkede. Hos de 

 Heste Exemplarer har Spidsen af Halepladen et lidet 

 Indsnit i Midten, hvorved dannes 2 korte Ende- 

 lapper, der ofte er asymetriske (se Fig. 27). 



De sammensatte Øine har, som ovenfor anført, 

 sin Plads paa den mest fremragende Del af Hovedets 

 Dorsalside (se Tab. XI, Fig. 1 og 3, Tab. XIII, Fig. 

 1 og 2). De er, i Modsætning til hvad Tilfældet er 

 hos Branchipodiderne, sessile, af nyredannet Form, 

 og saaledes stillede, at deres Forende ligger nær 

 sammen, medens der bagtil mellem dem er et større 

 Kum, der indtages af et ovalt, noget ophøiet og 

 skarpt begrændset Felt, den saakaldte Postocular- 

 knude (Tab. XIII, Fig. 1, x, Fig. 8). Umiddelbart 

 foran de sammensatte Øine ligger det enkle Øie 

 (Fig. 1, 5, oe), som dog ialmindelighed kun iitydeligt 

 skinner igjennem Integumenterne. Hvad de sammen- 

 satte Øines Bygning angaar, saa stemmer denne 

 idethele naar afsees fra deres sessile Character, 

 overens med samme høs Branchipodiderne, skjondt 

 ogsaa visse Uoverensstemmelser kan paavises Fra 

 det mørkebrune Pigment sees tal rige stærkt lysbry- 

 dende Legemer at straale ud til alle Sider. Disse 

 Legemer er den ydre Del af Krystalkeglerne, hvis 

 indre spidst udtrukne Del er dybt indplantet i Pig- 

 mentet. Enhver Krystalkegle viser sig ved nærmere 

 Undersøgelse (Fig. 6, 7) at være sammensat af 4 

 Længdesegmenter og forbinder sig indad med den 

 tværstribede Synsstav, hvortil igjen slutter sig en 

 af de mange Endefibre, hvori Synsnerven oploser 

 sig. Ethvert Synselement er isoleret ved en mem- 

 branos Skede, i hvis Midte sees 2 tydelige, jevn- 

 sides liggende Kjerner (Fig. 7), 



Første Par Følere (Tab. XII, Fig. 1, a ', Fig. 2) 

 udspringer paa Hovedets Ventralside til hver Side 

 af Overlæbens Basis og umiddelbart bag den halv- 

 maaneformige Pandeduplicatur. De er meget smaa 

 og ialmindelighed rettede skraat udåd og fortil, idet 

 de boier sig om Bagkanten af den ovennævnte 



ding posteriorly between the bases of the 2 caudal 

 filaments. 



This lamella, which is peculiar to the genus 

 Lepidurus, is generally, in the present species, of 

 comparatively small size, measuring as a rule no 

 more in length than the last caudal segment does 

 in breath. The shape is more or less decidedly lin- 

 guiform, without any noticeable constriction at the 

 base. It also varies very much both in size and 

 shape, as will be seen from the figures here given 

 (figs. 23 — 27), and generally increases in length with 

 age. Fig. 25 represents the caudal lamella of an 

 unusually large specimen ; but it is very seldom 

 that it attains to so considerable a size as that here 

 .shown. The caudal lamella in all specimens has 

 mediallj' a blunt keel armed with a rather variable 

 number of coarse denticles, generally 2 or 3. The 

 edges are coarsely and rather irregularly dentated 

 in their outer portion. In most specimens there is 

 a small indentation in the middle of the extremity 

 of the caudal lamella, thus forming 2 short, termi- 

 nal, often asymmetrical lobes (see fig. 27). 



The compound eyes, as above stated, are situ- 

 ated on the most prominent part of the dorsal sur- 

 face of the head (see PL XI, figs. 1, 3; PL XIII, 

 figs. ], 2). Unlike tliose in the Branchipodidæ, they 

 are sessile, reniform in shape, and so placed that 

 their anterior ends lie close together, while between 

 them posteriorly there is a considerable space which 

 is occupied by an oval, somewhat elevated and 

 sharply-defined field, the so-called post-ocular tubercle 

 (PL XIII, fig. 1 X, fig. 8). Immediately in front of 

 the compound eyes lies the ocellus (figs. ], 5, oc); 

 which, however, is generally only indistinctly seen 

 through the integuments. With regard to their 

 structure, the compound eyes, setting aside their 

 sessile character, agree with those in Branchipodidæ, 

 though a few points of difierenee can be found. 

 Numerous strongly refractive bodies are seen radi- 

 ating to all sides from the dark brown pigment. 

 These bodies are the outer part of the crystalline 

 cones, the inner pointed pai't being buried deeply 

 in the pigment. Each crystalline cone proves, on a 

 closer examination (figs. 6, 7), to be composed of 

 4 longitudinal segments, and to connect itself interi- 

 orly with the transversely barred ocular rod to 

 which, again, one of the numerous terminal fibres, 

 into which the optic nerve resolves itself, is at- 

 tached. Each visual element is isolated in a mem- 

 branous sheath, in the jniddle of which are seen 2 

 distinct nuclei lying side by side (fig. 7). 



The first pair of autennæ (PL XII, fig. 1, a\ 

 fig. 2) spring from the ventral surface of the head 

 on each side of the base of the upper lip, and imme- 

 diately behind the crescent-shaped frontal duplica- 

 ture. They are very small, and are generally di- 

 rected obliquely outwards and forwards, bending 



