RESPIRATORY ORGANS IN ARANEiE. 
31 
least as long as the two-celled columns of the septa, in order 
to allow sufficient space for the blood-corpuscles to pass 
between the ventral saccule and the outer hypodermis. 
Two authors, Locy and Jaworowski, deal with the formation 
of the definite lung-septa from the embryonic epithelia. 
According to Locy (’86), whose account differs from mine, 
the nuclei, which are in parallel rows, become plano-convex 
and arrange themselves in pairs, the convex side of each 
nucleus in one row being exactly opposite that of an adjacent 
parallel row (i. e., of an adjacent epithelium). Ultimately 
the cells of each pair of nuclei, which thus face each other, 
come in contact and fuse together to form the columns. 
’I’lie cells of such a pair of rows constitute the two walls of a 
flat, hollow sac, a respiratory lamella (i. e., a septa). Blood 
has a free access to the lamelhn at their anterior attachments. 
(Locy’s statement that a septa represents a hollow sac is, of 
course, incorrect. He apparently considers them attached at 
their anterior ends only.) 
Jaworowski’s account (’94, pp. GO-Gl), is more in agree- 
ment with mine. According to him the space between the 
two layers of nuclei of a septum is filled with protoplasm and 
tlie lacuna) appear between the cells, and are at first small 
and roundish, and later on large and elongate. Jaworowski 
evidently intends to imply that the columns are the remains 
of the protoplasm left between the lacunae, and his fig. 12 
illustrates this very clearly. Here two, or even three nuclei 
may be observed at one or both ends of a column at first, but 
later on this is rarely or never the case, only one nucleus 
being found at each end of the column (in agreement with 
Locy). 
The chitinous lining of the pulmonary saccules. — Shortly 
before the appearance of the lacuna) the walls of the saccules 
appear to collapse, and on the surfaces of contact, where the 
cavity was situated, two chitinous membi’anes are secreted. 
These pass over into one another at their medial, lateral, and 
anterior edges, so as to form a flattened chitinous .saccule 
within the epithelial saccule, and are further connected by 
