1909.] NATURAL SCIENCES OF PHILADELPHIA. 311 



of the same appendage but to one side of the stigma, where there is a 

 closed tube beneath the outer ectoblast formed by overgrowth in 

 the manner described by Janeck. Fig. 5 represents a stage still later ; 

 the whole pulmonary appendage has become flattened down to the sur- 

 face of the abdomen, the primary lamella? {Lam. 1) are not more than 

 two in number and only slightly pronounced, while the anterior end 

 of the pulmonary ingrowth is growing larger in the cephalad direction. 

 In fig. 6, cut to one side of the stigma (so comparable with fig. 4 of an 

 earlier stage), the anterior region of the solid ingrowth is divided into 

 two parts, the beginning of the first two true or secondary lamellae 

 {Lam. 2). The slightly later stage of fig. 7 is particularly instructive. 

 The abdomen now makes a short angle with the cephalothorax, so 

 that the layer of ectoblast {Ed.) most to the left in the figure is the 

 lining of the cephalothorax. The pulmonary stigma {P. St.) occupies 

 the same relative position as in fig. 5, but the pulmonary sac or cavity 

 {P. Cav.), which is lined on all sides by ectoblast, has become more 

 voluminous and anterior extensions of it lead into three secondary 

 lamellae {Lam. 2). There is no longer any trace of the primary lamellae. 

 These had become gradually shorter in the successive stages, shown 

 in figs. 2, 3, and 5, being only faintly marked in the last. There 

 is no trace of them in the stage of fig. 7 ; were they present they should 

 show just above the stigma {P. St.) on the mesial (right) side of the 

 ectoblastic operculum. The primary lamellae have not become the 

 secondary lamellae {Lam. 2), for the latter are directed cephalad and 

 arise, as we have seen, from the solid anterior portion of the pulmonary 

 primordium. These results are in essential agreement with those of 

 Janeck, though in the form studied by him, Lycosa, the primary 

 lamellae are larger and more numerous, and by the fusion of their free 

 ends with the mesial wall of the lung cavity give rise to a series of small 

 cavities lined by ectoblast which ultimately close up. The primary 

 lamellae do not become the lamellae of the adult, and, as Janeck has 

 indicated, would seem to have no more morphological importance than 

 the slight integumentary folds found on the mesial side of the proxi- 

 mal portion of the cephalothoracal appendages. 



The history of the secondary or definitive lamellae is as follows. 

 Arising from the solid anterior region of the lung tissue, as shown in 

 figs. 6 and 7, these lamellae become larger and more cylindrical with 

 narrower lamina {Lam. 2, fig. 8). Successive ones are formed from the 

 solid mesial wall of the lung ingrowth, and in their growth they press 

 into an archiccelic cavity (J5/. Cav.) between the ectoblast {Ed.) and 

 mesoblast {Mes.). In fig. 9, PI. XII, three of these secondary lamellae 



