§ 277. 
remains as a visual organ during the whole life; while, with other Lophy- 
ropoda, and with the Phyllopoda, it either entirely disappears, or remains. 
in a condition apparently rudimentary, by the side of the other eyes, which 
are subsequently formed. With certain Ergasilina,® and some’ Lopby- 
ropoda,® with the Caligina,“” and the males of some parasitic Isopoda,™ 
there are two permanent eyes, right and left, on the vertex of the head.. 
The Poecilopoda, also, have, beside their compound eyes, two simple ones,’ 
contiguous on the middle of the forehead.“ These simple eyes are also some- 
times the more numerous, and are then situated on each side of the head, 
in fours, sixes or eights, in a single or double row, constituting i' > Ocude 
seriati, as is observed with some Myriapoda; or they are collect ina 
thick group of twenty to forty, constituting the Oculi gregati, as is the case 
826 THE CRUSTACEA. 
with other Myriapoda, and with the Isopoda.* 
Each of these eyes has a 
separate branch of the optic nerve; this nerve, therefore, divides as many 
times as there are eyes. 
Another form of eyes which is pretty common among Crustacea, but 
which has many modifications, has received the name of Compound Ua- 
faceted Hyes. 
These organs are composed of a common cornea, covering numerous 
simple eyes, closely set against each other. 
They are found in their sim- 
plest form, with the Cirripedia at a certain epoch of development, with 
the Argulina, the Laemodipoda, and certain Lophyropoda, Phyllopoda, 
and Amphipoda. 
6 Lamproglena, Ergasilus (Nordmann, loc. 
cit. Tab. IT. fig. 1,7), Cyclops, Cyclopsina, Cy- 
pris, &c. 
7 With Limnadia, and Isaura, it is replaced by 
& compound eye ; see Joly, Ann. d. Sc. Nat. XVII. 
Pl. LX. fig. 39-41. 
8 This is so with the adult individuals of Apus 
and the Branchiopoda, where the simple embryonic 
eye persists inan atrophied condition between the 
two faceted eyes; see Schaffer, Der krebsartige 
Kiefenfuss, Taf. IL. fig.1¢., and Taf. V. fig. 3-5 ; 
also, Zaddach, loc. cit. p. 48, Tab. II. fig. 18-22, C. 
and Tab. IV. (Apus); Prevost, in Jurine’s Hist. 
d. Monocles, Pl. XX.-XXI. (Chirocephalus), and 
Joly, loc. cit. XIII. Pl. VII. (Artemia). The 
black spot observed front of the compound eye, 
with Lynceus, and certain species of Daphnia, is 
certainly only the remains of the simple eye ; see 
Muller, Entomostr. Tab. IX.-XI., and Jurine, 
Hist. d. Monocles, Pl. XV.-XVI. 
But, with this simple rudimentary eye, should 
not be ded the prot ical vesiculiform 
organ which is found behind the compound eyes of 
certain Phyllopoda and Lophyropoda. With Apus, 
this organ contains a nucleus, divided into four 
parts (Schaffer, ioc. cit. Taf. IL. fig. 1, b., or Zad- 
dach, loc. cit. p. 48, Taf. IL. fig. 10. P., 25). 
The vesiculiforra body which, with Limnadia, 
stretches from the inner surface of the head, be- 
hind the eye, towards the forehead (Brongniart, 
loc. cit. p. 83, Pl. XIII. fig. 6), may serve, accord- 
ing to Straus, to fix the animal to foreign bodies ; 
(see Mus. Senckenb. II. p. 126, or Férussac, Bull. 
* [ § 277, note 8.] “With Artemia and Branchi- 
pus, Leydig (loc. cit. Siebold and Kélliker’s 
Zeitsch. II. p. 295) has found very highly-devel- 
oped eyes. In structure they correspond to the 
compound faceted eyes described below. In re- 
gard to the pigment-spots found on the head of 
these animals, and regarded as of a visual charac- 
ter by Joly and others, this observer considers 
Here, directly under the cornea, are a greater or less 
d. Sc. Nat. XXII. 1830, p. 333). With Evadne, 
there is found at the same place, behind the large 
eye, a circular muscle, which also, perhaps, is for 
the attachment of the animal.* 
9 Nicothoé (Rathké, Nov. Act. Nat. Cur. XX. p. 
102, Tab. V. fig, 1,8, 10). 
10 Hersilia, Peltidium, &c. (Philippi, in Wieg-: 
mann’s Arch. 1839, I. p. 128, Taf. [V. fig. 9, 15, 
or Milne Edwards, Hist. d. Crust. Pl. XXXVIL). 
ll Pandarus, Caligus, Trebius, Dinematura, 
&c. (Milne Edwards, Hist. d. Crust. Pl. 
XXXVIIL., and Kréyer, in the Naturhist. Tidskr. 
I., or in the Isis, 1841, p. 188, Taf. I.). 
12 Phryzus and Bopyrus (Rathké, Nov. Act. 
Nat. Cur. XX. p. 44, Tab. I. fig. 13, in Tab. II. fig. 
8, and, De Bopyro et Nereide, Tab. I. fig. 2). 
13 See Van der Hoeven, Recherches, &c., 23, 
Pl. III. fig. 5, a. a., 6, C. 
14 With Platyulus, there are, on each side, six 
eyes, arranged in two rows. Scolopendra has 
four, while with Glomeris, there are eight, which 
form a simple arcuate row on each side ; see Miul- 
ler, in Meckel’s Arch. 1829, p. 40, Tab. III. fig. 
3, 4, also Kutorga, loc. cit. p. 17, Tab. III. fig. 3, 
4 (Scolopendra), and Brandt, Mediz. Zool. II. 
p. 99, Laf. XV. fig. 43 (Glomeris). 
15 Treviranus, Vermisch. Schrift. II. p. 32, 
Taf. VIL. fig.1 (Lithobius) and Muller, in Meck- 
el’s Arch. 1829, p. 43 (Judus) ; see also T'revi- 
ranus loc. cit. L. p. 64, Taf. IX. fig. 54 (Porcellio), 
Muller, loc. cit. p. 42, Taf. III. fig. 5, 6 (Cymo- 
thoa), and Lereboullet, Ann. d. Sc. Nat. loc. cit. 
p. 107, PL. IV. fig. 2, 2°. (Lygidium). 
them as mere of pigment gr les, 
having no special function whatever. This natu- 
ralist alludes, also, to the problematical body above 
mentioned. He did not observe it with Artemia, 
but it was present with Branchipus, and larger in 
the larval than in the adult conditions. He hesi- 
tates to express an opinion as to its nature. — Ep, 
