2 
W. F. PUECELL. 
PAGE 
VI. The Development of the AEclominal Longitudinal Muscles 
and their Tendons . . . . 4F 
VII. The Entapophyses (Ectodermal Tendons) of the Pul- 
monary Segment . . . .47 
The Inteii^xilmonary (Epigastric) Fold in the Adult of 
Attus . . . . . 4h 
The Inteipulnionary Fold in other Spiders . . iiO 
VIII. The Development of the Trachea; and the Entapophyses 
of the Tracheal Segment . . . 53 
The Post-embryonic Development of the Tracheal 
Plate . . . . .57 
Critical Remarks on the Literature . . .61 
Tlie Attus Type and Similar Types of Tracheae in 
Other Spidei's . . . . .62 
The Agelena Type of Trachea; and its Develoiunent . 63 
The Tracheae in the Dysderidae . . .68 
Tiie Tracheae in Argyroneta aquatica . . 70 
The Tracheae in the Scytodidae. Palpimanida*. and 
Filistatidae . . . .71 
IX. The Entapophyses of the Third and Fourth Abdominal 
Appendages (the S 2 >inners) . . .74 
X. General Conclusions . . . .75 
The Origin of the Tendinal or Medial Tracheal Trunks 
in Araneae . . . . .76 
The Origin of the Lateral Tracheal Trunks in Araneae 78 
The Origin of tlie Secondary Tracheal Tubules . 80 
The Origin of the Lung-books in Arachnids . . 81 
The Homologies of the Pulmonary Segments in 
Arachnids . . . . .85 
XI. Historical List of Papers concerning the Lung-books of 
Arachnids . . .02 
List of Literature . . . .06 
Exf)lanation of the Plates . . .103 
I. Introduction. 
It is just one hundred years ago that the first anatomical 
account of the lung-books of Arac hnida was published by 
Meckel (’09), who, like his immediate successors, looked upon 
these organs as gills, and it was not until 1828 that their 
pulmonary nature was recognised by Johannes Muller (’28a, 
’28b) and Straus-Durckheim (’28j. The latter was also, 1 be- 
