26 ARACHNIDA. 



tlie exterior (Fig. 14 B). Kowalevsky and Schulgix, who also 

 noticed them, referred them, though with some hesitation, to the 

 splanchnic layer of the mesoderm. Laurie's account would rather 

 tend to show that they arise from the somatic layer, as do the coxal 

 glands of the Scorpiones and the nephridia of the Annelida (Vol. i., 

 Fig. 137, p. 297). The nephridial character of the efferent genital 

 ducts seems to he confirmed by the fact that they open into the body- 

 cavity in the form of a wide funnel (Kowalevskt and Schulgin" 

 [Brauer]). Laurie also believes that at least in part they are 

 nephridial in origin. The ends of the canals which are directed 

 outwards long remain closed, a fact which we do not regard as 

 disproving the nephridial character of the efferent ducts, since even 

 the Annelidan nephridia develop in a similar way. 



From Laurie's description we might imagine that the mesodermal efferent 

 ducts become directly connected with the ectoderm at the points where the 

 remains of the first pair of abdominal limbs lie in the form of ectodermal 

 thickenings (Fig. 14 B, g.op), as is the case, according to Beegh, with the 

 nephridia of the Annelida. Kowalevsky and Schulgix, however, speak of an 

 ectodermal invagination, towards which the mesodermal efferent duct grows, se- 

 as to unite with it. This invagination, as far as can be made out from their 

 short account, is small, and it appears very possible that such an ectodermal 

 invagination might arise at the thickening which indicates the position of the 

 abdominal limbs. An ectodermal termination has also repeatedly been assumed 

 for the nephridia and the genital efferent ducts of the Annelida. It is, however, 

 highly probable that the short unpaired portion is derived from a depression of 

 the ectoderm. In the Pedipalpi this unpaired segment is much larger, and 

 becomes a large cavity (No. 31). 



The genital glands arise, according to Kowalevsky and Schulgix, as cell- 

 thickenings "apposed to the inner tube." This can only be understood to mean 

 that a part of the peritoneum (i.e., of the secondary body-cavity) is concerned 

 in the formation of the genital organs ; on this point, however, as well as on 

 the differentiation of the mesodermal structures, we await further particulars.* 



II. Pedipalpi. t 



According to Bruce, who has made a few statements as to the ontogeny of 

 Pkrynus, the embryo here, as in the Scorpiones, has an embryonic envelope. 

 We may indeed make the general assumption that the course of development in 

 the Pedipalpi resembles that in the Scorpiones. Bhuce points out as specially 

 remarkable the existence of a sensory organ at the base of the second ambulatory 

 limb, consisting of columnar cells prolonged externally into filaments. 



The Pedipalpi are very closely related to the Scorpiones, and, like 

 the latter, show in their organisation many points of agreement with 



* [See footnote, p. 3. — Ed.] 



t [The Pedipalpi are oviparous ; the eggs are carried in a gelatinous sac 

 attached to the ventral surface of the mother. For chief ontogenetic features 

 see App. Lit. Pedipalpi, Nos. I. -III., noting presence of reversion of germ-bands 

 and unanimous conclusion that Pedipalpi are more nearly related to the Araneae 

 than to the Scorpiones. — Ed.] 



