896 THE ARACHNOIDAE. $ 320. 
rudimentary penis. It is yet undetermined if the two external, lateral, 
pectiniform appendages situated near the genital orifice in both sexes, 
serve any purpose during copulation. 
§ 320. 
We have, as yet, only insufficient observations on the Development of the 
Arachnoidae. However, those that we possess upon its first stages,” show 
that, with few exceptions,” here as with the Crustacea, the disappearance 
of the germinative vesicle is followed by a superficial and partial segment- 
ation of the vitellus. There is thereby formed a thin embryonic layer, com- 
posed of molecular corpuscles retained in a transparent viscid liquid, and 
distinguished from the rest of the vitellus by its white color. While this 
oval blastoderma, whose longitudinal axis corresponds to the ventral or 
nervous side of the embryo, extends towards the sides and the back, it 
divides into an external or serous, and an internal or mucous lamella, 
the last of which gradually covers the remaining portion of the vitellus, 
and becomes changed into the digestive tube and its appendages. In 
the mean while, there appear, on the external surface of the serous lamella, 
various symmetrical prominences and projections, which in time become 
the segments of the body, the parts of the mouth, the tactile, and the 
locomotive organs. 
With the exception of the Scorpionidae, and Oribatea, which are vivi- 
parous, the embryos of all the Arachnoidae are developed subsequent to the 
deposition of the eggs. 
With the majority of Arachnoidae, the embryos, at their escape from the 
egg, have the form of the adult.“ 
The lower orders, only, form an 
exception in this respect, for they acquire their definite form after several 
moultings, and a true metamorphosis. 
10 Tulk (Ann. of Nat. Hist. XV. p. 56) has 
lately expressed the opinion that these combs serve 
to clean the palpi, the tarsi, and the extremity of 
the tail. He adduces, as proof, the presence of 
transparent combs of exactly identical form, with 
Obisium, between the pincers of the cheliceres, and 
which are used for this purpose. 
1 The first phases of development have not 
been observed as yet except with the Araneae and 
Scorpionidae ; see Herold, De Generat. Aranear. 
in ovo, 1824; Rathké, Zur. Morphol. Reisebemerk. 
aus Taurien, 1837, p. 17, and in Burdach’s 
Physiol. II. 1837, p. 242; the same in Froriep’s 
neue Notiz. XXIV. 1842, p. 165 (Lycosa sac- 
cata) ; also Kélliker, in Mnuiller’s Arch. 1843, p. 
139 (Scorpio europaeus) ; finally, Wittich, Observ. 
quaed. de Aranear. ex ovo evolut., Halis. 1845, fig. 
1, A. As to the development of the Acarina, I 
have satisfied myself upon the eggs of the Oribatea, 
*[§ 320, note 1.) See, also, Wilson, Researches 
into the structure and develop. of a newly-discov~ 
ered parasitic Animalcule, &c., in the Philos. Trans. 
1844, p. 805 (Entozoon (Demodez) folliculorum), 
and Van Beneden, Recherches sur |’Atax upsilo- 
phora, in the Mém. de l’Acad. Roy. de Bruxell. 
XXIV. Wilson’s details are imperfect, and throw 
but little light on the real character of the develop- 
ment of the follicle-parasite. It would appear, 
however, to be truly one of the Arthropoda. — Ep. 
t [§ 820, ncte 2.) For the embryology of the 
With the Pycnogonidae, these 
that the same phenomena occur as with most of the 
other Arachnoidae.* 
2 [ have distinctly seen, in the eggs of Macrobi- 
otus Hufelandii, the segmentation involve the en- 
tire vitellus. Kéldiker (Miller's Arch. 1843, p. 186) 
has made the same observation with Pycnogonum.t 
8 The relations of the Scorpionidae in this respect 
are very remarkable, for their embryos are devel 
oped in the ovaries at the spot even where the egg 
are formed ; see Mid/er, loc. cit. p. 55, and Rathké, 
Zur Morphol. loc. cit. It is evident that the sperm 
must ascend from the two seminal reservoirs inte 
the ovaries to fecundate the eggs. With the Ori- 
batea, the embryos appear to be developed in a 
kind of uterus situated immediately behind the 
ovipositor. 
4 With the Araneae, the sexual differences which 
are so striking do not appear until after the first 
moulting. 
Tardigrada, see Kaufmann, loc. cit. in Siebold 
and Kélliker’s Zeitsch. III. 1851, p. 220. The 
type of development is like that of the Articulata in 
general, and this would seem to clearly settle the 
position of these animals in this class. Kauf- 
mann confirms the observation of Siebold as to 
the segmentation of the entire vitellus. After this 
process has occurred, the mulberry like mass is 
changed into the embryo, exactly as is observed 
with the eggs of the Arachnoidaein general. — Ep. 
