310 PROCEEDINGS OF THE ACADEMY OF [May, 



there is a saccular invagination, from which proceeds dorsally a tube 

 dividing into several branches; "it is, however, clear that the so-called 

 lungs of the spider in the embryonal condition are repeatedly branched 

 trachea?." These tracheal tubes ultimately disappear, and the de- 

 finitive pulmonary lamellae arise from parallel outgrowths of the vesti- 

 bule (Vorraum). 



Finally, the latest memoir, that of Janeck (1909) on Lycosa, is 

 the most extensive, and he had not only an excellent series of stages, 

 but he also made use of wax reconstructions. He describes thoroughly 

 the infolding of the first abdominal appendage, finds that it develops 

 a series of pronounced folds on its inner (mesial) surface, thus far 

 essentially corroborating the observations of Simmons and Purcell, 

 but, contrary to these writers, he finds these embryonic folds disappear. 

 "Especially important is the demonstration that the folds of text 

 figure 16, which many authors refer directly to the lung-leaves, have no 

 relation at all to the lung . . . and the fold formation of these stages 

 show themselves to be not even forerunners of the lung-leaves." The 

 pulmonary lamella? arise as secondary folds from a compact lung mass. 



It will be seen that there are considerable differences of opinion, out 

 of which it is hard to reach the true state of affairs. My observations 

 are in entire disagreement with the conclusions of Schimkewitsch and 

 Jaworowski, that the lungs arise as tubular tracheae, and I believe 

 that Jaworoski misinterpreted embryonic dorso-ventral muscles. 

 Then neither of these authors described the earliest stages. With 

 Purcell, I find folds appearing upon the posterior surface of the pulmo- 

 nary appendages before it invaginates ; but, in opposition to him and 

 Simmons, and in agreement with Janeck, I find these folds are only 

 temporary, and that the definitive lamella? arise from a disassociated 

 solid cell mass. Locy, Morin and Kishinouye were correct, so far as 

 their observations went. 



In Theridium, about the stage of reversion, the pulmonary stigma 

 (P. St., fig. 1, PI. XI) is present as an ectoblastic invagination just behind 

 the appendage of the second abdominal segment, and on the posterior 

 face of this appendage are present three folds (Lam. 1). These embry- 

 onic folds may be called the primary lamella?. In a later stage, shown 

 in fig. 2 (a surface view of this stage is represented in fig. 16, PI. XII), the 

 pulmonary stigma (P. St.) has become deeper, and the primary 

 lamella? (Lam. 1) more pronounced. Later, fig. 3, the pulmonary sac 

 or chamber has become a narrow space by the further insinking of the 

 pulmonary appendage. Two primary lamella? can be still distinguished 

 (Lam. 1) but they have become relatively smaller; fig, 4 is a section 



