322 Tbos. II. Montgomery. 



largest, and these will form the spinnerets, but have not yet produced 

 glandular ingrowths. The second pair of appendages are the smallest 

 and are connected on each side by an oblique ridge with the first 

 pair (Fig. 8G). The first pair of abdominal appendages, those of 

 the second segment, are beginning to invaginate as the lung books ; it 

 is interesting to note that primaiy lamellae arise simultaneously with 

 the deepening of the lung sac, shown on surface view in Fig. 86, and 

 on sections in Figs. 91c, 92, 93, Pul. C. denoting the lung cavity and 

 Pul. L. the primary lamellae. Fig. 93 is a section through the 

 fourth leg {L. 4), the first abdominal ganglion {Ab. 1 G.), the lung 

 book and the third and fourth abdominal appendages {Ab. db. Ah. 

 4.b) ; and Fig. 91c through the lung book and a portion of the third 

 abdominal segment (Ab. 3). Figs. 89 and 91a also exhibit the early 

 lung books. Each lung book has three lamellae composed of ectoblast. 

 The tail lobe at the earlier part of the reversion {Caud., Fig. 81) is 

 still somewhat posterior to the appendages, but subsequently (Figs. 

 82, 84, 86) it moves forward to about their level. Its shape is seen 

 best in Figs. 84 and 85, and its terminal apex is elevated above the 

 surface of the embryo (Fig. 91b). This tail lobe represents the 

 fusion of the caudal lobe proper (telson) with the three posterior 

 abdominal segments. There is still no proctoda^al invagination. 



The nerve ganglia of the thorax (Figs. 89, 91a) are contiguous, a 

 composite of those of the pedipalps {Fed. G.) and the four legs (L. 1 

 G.-L. 4 G.). The first abdominal ganglion {Ah. 1 G., Fig. 89) seems 

 to be fused with the other abdominal ganglia forming a compound 

 ganglion united with the most posterior thoracal. All these ganglia 

 are still connected with the superficial ectoblast. 



All cephalic and thoracal mesoblast sacs are shown in Fig. 91a. 

 The rostral sacs are the largest in the embryo {R. Coel., Figs. 87a, b, 

 89-91a), they bound the cerebral ganglia {Ce. G., Figs. 89, 91a) 

 posteriorly and these and the cheliceral ganglia laterally (Fig. 87a), 

 are continued into the rostrum {Bos., Figs. 89-91a) and along the 

 dorso-anterior aspect of the stomodaeum. These are very voluminous 

 sacs, but much folded by the invagination of the several parts of the 

 brain. They meet in the midline within the rostrum and along the 

 antero-dorsal border of the stomodaeum (Fig. 90), also dorso-posterior 



