396 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 haye, 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. With the Pycnogonidae, these 



^0 Talk (Ann. of Nat. Hist. XV. p. 56) has that the same phenomena occur as with most of the 



lately exjiressed the opinion that these combs serve other Arachnoidae.* 



to clean the palpi, the tarsi, and tlie extremity of - I have distinctly seen, in the eggs of Macrobi- 

 the tail. He adduces, as proof, the presence of otus Hufelandii, the segmentation involve the en- 

 transparent combs of exactly identical form, with tire vitellus. Kolliker (Miiller's Arch. 18-13, p. 136) 

 Obisium, between tlie pincers of the cheliceres, and has madejthe same observation with Pycnogonum.i 

 which are used for this purpose. 3 The relations of the Scorpionidae in this respect 



1 The first phases of development have not are very remarkable, for their embryos are devel- 



been observed as yet except with the Araneae and oped in the ovaries at the spot even where the eggs 



Scorpionidae ; see Herald, De Generat. Aranear. are formed ; see Miil/er, loc. cit. p. 55, and Rathki, 



in ovo, 1824 ; Rathki, Zur. iMorphol. Reisebemerk. Zur Jlorphol. loc. cit. It is evident that the sperm 



aus Taurien, 183V, p. 17, and in Biirdach's must ascend from the two seminal reservoirs into 



Physiol. II. 1837, p. 242 ; the same in Froriep's the ovaries to fecundate the eggs. With the Ori- 



neue Notiz. XXIV. 1842, p. 165 {Lycosa sac- batea, the embryos appear to be developed in a 



cata) ; also Kolliker, in MuUer^a Arch. 1843, p. -kind of uterus situated immediately behind the 



139 {Scorpio europaeus) ; finally, fVittich, Observ. ovipositor. 



quaed. de Aranear. ex ovo evolut., Halis. 1845, fig. 4 With the Araneae, the sexual differences which 



1, A. As to the development of the Acarina, I are so striking Jo not appear until after the first 



have satisfied myself upon the eggs of the Oribatea, moulting. 



* [§320, note 1.] See, also, JFiVson, Researches Tardigrada, see Kmifmann, loc. cit. in Siebold 



into the structure and develop, of a newly-discov- and Ktilliker^s Zeitsch. III. 1851, p. 220. The 



ered parasitic Animalcule, &c., in the Philos. Trans, type of development is Uke that of the Articulata in 



lS44,p.3Q& {Entozoon(Demodex)folliculorum), general, and this would seem to clearly settle the 



and ymi Beneden, Recherches sur I'Atax upsilo- position of these animals in this class. Kauf- 



phora, in the Mem. de I'Acad. Roy. de Bruxell. mann confirms the observation of Siebold as to 



XXrV. Wilson's details are imperfect, and throw the segmentation of the entire vitellus. After this 



but Uttle light on the real character of the develop- process has occurred, the mulberry like mass is 



ment of the follicle-parasite. It would appear, changed into the embryo, exactly as is observed 



however, to be truly one of the Arthropoda. — Ed. with the eggs of the Araclmoidae in general. — Ed. 



t [ § 320, note 2.] For the embryology of the 



