RESPIRATOKY ORGANS IN ARANE.E. 
61 
Critical remarke on the literature. — Schimkewitscli was the 
lirst to figure a stage in the development of the trachea of a. 
spider, for in his Russian paper (’86a) he gives a sketch (fig. 
29a) of what is evidently the tendinal portion of the trachea 
{ect.) and the entochondrite {L. 2) attached to it. I am 
unable at j^resent to consult his principal paper on the 
development of Spiders (’87), but apparently Schimkewitscli 
failed to recogni.se the tracheal nature of the ectodermal 
tendon, ect., which he considered to be a provisional struc- 
ture, as is evident from the following remark in a later 
paper (’94, p. 210) : “ Bei den Araueinen, wo das Endoskelet 
im Abdomen fehlt, enstehen beim Embryo unter den hintern 
Sehnen provisorische Ectodermfalten, die von mir auf fig. 11, 
tab. 22 [’87] abgebildet sind.” By ‘^Sehnen” the author 
refers to the entochondrites of the ventral longitudinal 
muscles. 
Simmons (’94) gives two figures of the developing trachea. 
His earliest stage (fig. 8) is a sagittal section cut at a period 
when the tracheal appendages are on opposite sides of the 
embryo (my stage 5). It, therefore, represents a section 
through the dorsal proliferation of the tracheal sac, and is, as 
Simmons correctly claims, homologous with the pulmonarv 
sac. On the other hand, his second figure (fig. 9), cut after 
the reversion, evidently represents the tendinal portion of 
the trachea, and cannot be the same structure as that repre- 
•sented in fig. 8, ns Simmons claims it to be. 
Simmons also claims to have found rudiments of the pul- 
monary folds, and interprets certain undulations on the surface 
of the embryonic trachea and two iu-pushings at its ends 
(fig. 8) as such, but without, 1 think, sufficient justification 
for doing so. Similar undulations may be found in Attus 
floricola (e.g. on the posterior surface of appendage 2 in 
fig. 5), which certainly bear a superficial resemblance to the 
pulmonary folds in appendage 1, but these undulations are 
produced by the mitoses of nuclei lying quite near the surface, 
and may occur on any part of the body. They have certainly 
nothing to do with pulmonary folds. Also, the two in-pushings 
