58 ARACHNIDA. 



degenerate, while those of the fourth and fifth segments become 

 changed into spinning mammillae (Figs. 30 and 31, Salensky, Locy., 

 Morin). On these mammillae the spinning glands arise as ecto- 

 dermal invaginations (Fig. 46, spw, p. 88). If the spinning 

 mammillae are reduced limbs (p. 79), we must regard the glands as 

 belonging to the order of crural glands, having a phylogenetic origin 

 similar to that of the corresponding structures in Peripatus, the 

 Myriopoda and the Insecta. The anus arises oh the last abdominal 

 segment at the completion of flexure-reversal, when the post-abdomen 

 is already degenerating, as an ectodermal invagination. 



When the young Araneid leaves the egg-integument it is, in many 

 cases, quite incapable of movement. It continues for some time (in 

 many forms for some days) in the same place without any movement 

 being apparent in it. It is invested more or less closely by a 

 structureless envelope, the first embryonic cuticle, beneath which the 

 future hairy covering is already present. This outer cuticular 

 envelope, which may to some extent be regarded as a larval integu- 

 ment, is broken through after a time, but the young Araneid is 

 still somewhat helpless ; it can, indeed, move its limbs, but it can 

 only move from place to place freely after several moults. The 

 young of Epeira cornuta, on the contrary, is able to move to a 

 considerable extent when it leaves the egg (Purcell). 



It is an interesting fact that the first cuticular integument may 

 be provided witli a kind of egg-tooth, which serves for splitting the 

 egg-shell. According to the researches of F. Purcell, there is, at 

 the base of the two pedipalps of Tegenaria domestica, a thickened 

 plate-like part of the first chitinous integument, which, in contrast 

 to the rest of the cuticular covering, appears dark in colour — almost 

 black. From this spot an outwardly projecting spine arises, such as 

 was described above as an egg-tooth. A similar but less developed 

 spine is found in a corresponding position in Attus floricola, and also 

 in a Xystims. It may also occur in other Araneids. Purcell 

 observed that the first rent takes place in the chorion, immediately 

 over the egg-tooth. It extends from this point, and soon a cap-like 

 portion of the egg-integument is separated off. The movements of 

 the embryo, which must take place to produce the splitting of the 

 egg-shell, coidd not be noticed. The spine, having fulfilled its 

 function in splitting the egg-integument, is thrown off with the 

 cuticular envelope. "We shall find a similar arrangement in the 

 Myriopoda, in which also an egg-tooth belonging to the cuticular 

 envelope develops. The same is the case in the Opiliones (p. 33). 



