122 0. L. Simmons — Development of Lungs of Spiders. 



specially concentrated arrangement of tracheal tubes. He 

 regards the tracheae, including the lungs of all " Tracheates " 

 as having their origin in dermal glands which have gradually 

 been modified for respiratory purposes. He also states that in 

 considering the relationships of these various forms, the limbs 

 are of so little importance that one might almost be tempted 

 to leave them out of account. In a later paper on " The 

 Chernetidae " Bernard ('93) repeats in substance his earlier 

 views. 



In a word, these authors, regarding the tracheal form of re- 

 spiration as the primitive — a premise which the observations 

 of Moseley on the tracheae of Peripatus seemed to render valid 

 — have looked upon the air tubes of the arachnids as the primi- 

 tive and the lungs as the derivative condition. 



The question thus brought into prominence can only be set- 

 tled by tracing the development of the respiratory organs of 

 the Arachnida. Several authors have touched upon this ques- 

 tion. Thus Locy ('86) describes the later stages of Agelena 

 ncevia as follows : The lungs arise as a pair of extensive invagi- 

 nations. In sagittal sections they appear as oblong plates of 

 cells with the nuclei in parallel rows. These nuclei are flat- 

 tened on one side and convex on the other. The cells of two 

 adjoining rows unite by the edges toward which the convex 

 sides of the nuclei project and thus a lamella is formed. Later 

 the nuclei of adjoining cells fuse, forming protoplasmic pillars 

 between which are the blood lacunae. Around each lamella is 

 a chitinous membrane — the ventral and the dorsal being con- 

 tinuous at the free (posterior) end of the lamella. The cells 

 of the ventral wall become arranged into two distinct layers. 

 A part of the development described takes place after the 

 hatching of the e<yg. 



A. T. Bruce ('86-87) says 'that a lung-book of a spider 

 may be regarded as an involuted appendage or appendages. 

 He noticed that the abdominal appendages become less con- 

 spicuous and that slight folds appear on their anterior faces. 

 He did not observe all the stages and, judging from his text 

 and figures, it is very evident that he was confused in some of 

 his interpretations. K. Kishinouye ('90) states that in the 

 basal part of the first abdominal appendage there is an ecto- 

 dermic invagination — not deep or large. The wall of this 

 pocket which faces the distal end of the appendage is thicker 

 and its cells become arranged in parallel rows. Two of these 

 rows, adhering to each other, produce a lamella. He confirms 

 Locy's description of the later stages. On the second abdomi- 

 nal appendage is another ectodermic invagination — a deeply 

 invaginated tube which remains in about the same state of 

 development until after hatching. The appendage shortens 



