EESPIRATORY ORGANS IN ARANE^. 
3 
lieve, the first to point out (p. 315) that the lung-books could 
be regarded as a special form of tracheae, a view which was 
later on elaborated by Leuckart (’ 48 , p. 119 note, and ’ 49 ) and 
for a time generally accepted, until the appearance of Ray 
Lankester’s paper, “Lim ulus: an Arachnid,” in 1881, opened 
up the probability of the branchial origin of these organs. 
While working at certain points in the embiyology of a 
spider some years ago it occurred to me that a more careful 
and detailed investigation of the development of the lung- 
books and tracheae than had hitherto been attempted would 
probably reveal some points of interest in connection with the 
origin of these organs, and indeed it soon appeared that two 
important facts had been entii’ely overlooked, viz. (1) the 
appearance of the earliest lung-leaves on the free 
posterior side of the provisional abdominal ap- 
pendages quite outside of the pulmonary invagi- 
nation, and (2) the origin of a considerable part of 
the trachem from ectodermal tendons (entapophyses) 
and not from lung-books. This latter appeared to me a 
point of particular interest, as it is the only case, I believe, in 
which the origin of a trachea from another organ not re- 
spiratory in nature can be clearly demonstrated. 
My investigations were carried out in the years 1894 and 
1895, in the Zoological Laboratory of the University at Berlin, 
and my thanks are due to Geheinn’ath Prof. F. E. Schulze 
for the use of his splendidly equipped laboi’atory. About one 
third of the text had already been written and most of the 
figures drawn when I left Berlin in 1895 for South Africa, 
where various circumstances prevented the completion of the 
paper for the press until quite recently. 
Material. — The material for the development was collected 
in the neighbourhood of Berlin, and consisted of the embryos 
and young of Sitticus (Attus^) floricola C. K., of which 
T had an unlimited supply of all the required stages of de- 
velopment. Besides these T examined a small number of 
* Tins name has been recently discarded by E. Simon and Sittici;s 
snb.stitnted in its stead. 
