- Denne Plade, der er eiendommelig for Slegten 
: Lepidurus, er hos nerveerende Art ialmindelighed af 
__ forholdsvis ringe Storrelse og som oftest ikke len- 
S. gere end sidste Halesegment er bredt. Formen er 
mere eller mindre udpreget tungedannet, uden nogen 
bemerkelig Indsnoring ved Basis. Den varierer for- 
ovrigt serdeles meget saavel i Storrelse som Form, 
a hvad der vil kunne sees af de her givne Figurer 
(Fig. 23—-27), og tiltager ialmindelighed i Lengde 
med Alderen. Fig. 25 fremstiller Halepladen hos et 
_ ganske useedvanlig stort Exemplar. Det er imidler- 
tid meget sjeldent, at den naar en saa betydelig 
___ Storrelse som her angivet. Langs efter Midten har 
_ Halepladen hos alle Individer en stump Kjol besat 
med et noget varierende Antal af grove Tagger, 
_ sedvanligvis 2 eller 3. Kanterne er i sin ydre Del 
grovt og noget uregelmessigt sagtakkede. Hos de 
____ fleste 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 Wine har, som ovenfor anfort, 
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 Modsetning til hvad Tilfeeldet er 
hos Branchipodiderne, sessile, af nyredannet Form, 
og saaledes stillede, at deres Forende ligger ner 
_ sammen, medens der bagtil mellem dem er et storre 
Rum, der indtages af et ovalt, noget ophoiet og 
 skarpt begrendset Felt, den saakaldte Postocular- 
-_ knude (Tab. XIII, Fig. 1, x, Fig. 8). Umiddelbart 
foran de sammensatte @ine ligger det enkle ie 
skinner igjennem Integumenterne. Hvad de sammen- 
satte Mines Bygning angaar, saa stemmer denne 
idethele naar afsees fra deres sessile Character, 
overens med samme hos Branchipodiderne, skjondt 
ogsaa visse Uoverensstemmelser kan paavises. 
det morkebrune Pigment sees talrige sterkt 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 neermere 
- Undersogelse (Fig. 6, 7) at vere sammensat af 4 
— Lengdesegmenter og forbinder sig indad med den 
erstribede Synsstay, hvortil igjen slutter sig en 
af de mange Endefibre, hvori Synsnerven oploser 
Ethvert Synselement er-isoleret ved en mem- 
s Skede, i hvis Midte sees 2 tydelige, jevn- 
ende Kjerner (Fig. 7), 
» Par Folere (Tab. XII, Fig. 1, a', Fig. 2) 
paa Hovedets Ventralside til hyer Side 
ns Basis og umiddelbart bag den halv- 
Pandeduplicatur. De er meget smaa 
hed rettede skraat udad og fortil, idet 
om Bagkanten af den ovennevnte 
(Fig. 1, 5, oe), som dog ialmindeligled kun utydeligt 
Fra 
| ding posteriorly between the bases of the 2 candal 
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 mnch 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 candal 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 
medially 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. XII, 
figs. 1,2). Unlike those in the Branchipodide, 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. 1, 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 Branchipodide, 
though a few points of difference 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 part 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 middle of which are seen 2 
distinet nuclei lying side by side (fig. 7). 
The first pair of antenne (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 
