OPILIONES. 33 



closely for us to decide whether this is also the case in them. Faussek found 

 in embryos in which the segmentation of the germ-band is commencing, an 

 accumulation of cells at the posterior end of the band, which strongly resembles 

 the point of ingrowth in the germ-band of the Scorpiones. The statements 

 hitherto made as to the nature of this structure are, however, so contradictory 

 that it is impossible to gain any clear idea of it. Faussek derives these cells, 

 which appear like a thickening of the blastoderm, from a deposit of yolk-cells 

 on the blastoderm. At first he derived the genital glands from this deposit, 

 i.e., from yolk-cells, but he afterwards traced them to a thickening of the 

 blastoderm which appeared at a very early stage. A more exact account of 

 the partly contradictory statements on this subject may be expected in 

 Faussek's larger work [App. to Lit. on Opiliones, Nos. III. and IV.] 



The mesoderm, so far as we can gather from the few statements 

 on the subject, splits into a somatic and a splanchnic layer, so that 

 in this respect also there is resemblance with the Scorpiones and the 

 Araneae. 



The enteron seems to form as in the Araneae, apart from the origin 

 of the entoderm, which arises differently according to Faussek. The 

 yolk is directly surrounded by the splanchnic layer of the mesoderm, 

 and the yolk-cells now become applied to this layer, eventually 

 giving rise to the continuous epithelium of the enteron. This 

 process commences in the anterior part of the body. 



We have only a few isolated statements as to the further develop- 

 ment of the Opiliones. Metschnikoff (No. 34, p. 520) traces the 

 origin of the abdominal limbs, and Balbiani describes a few of the 

 later ontogenetic stages. It appears that the cephalo-thoracic seg- 

 ments to which the four pairs of limbs belong are distinctly marked 

 off from one another in the embryo, but this segmentation disappears 

 during the further course of development, and is not recognisable in 

 the adult. Between the eyes and the bases of the chelicerae lies an 

 unpaired, spine-like structure, which, like similar structures in the 

 Araneae, and especially in the Myriopoda (Chilognatha), we shall call 

 the egg-tooth (p. 58, and cf. the chapter on the Myriopoda). 



The little that is known of the ontogeny of the Opiliones is in 

 harmony with that of the Arachnida generally. An important 

 feature which is still recognisable in the adult, seems, according to 

 Balbiani, to be very marked in the embryo. This is the occurrence 

 of masticatory ridges on the pedipalps and on the two anterior pairs 

 of limbs. Herein we find a striking resemblance to the Scorpiones. 

 The Opiliones further resemble other Arachnida in the number 

 and position of the limbs, and in the presence of a coxal gland 

 \MacLeod), homologous with the synonymous organ in other Arach- 

 nids. Whereas, however, in other groups, this gland is merely 



D 



