214 Mr. O. L. Simmons on the 



paper on the Chernetida3 Bernard (1893) repeats in substance 

 liis earlier views. 



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

 respiration as the primitive — a premise which the observations 

 of Moseley on the trachete of Peripatus seemed to render valid 

 — have looked upon the air-tubes of the Arachnids as the 

 primitive and the lungs as the derivative condition. 



The question thus brought into prominence can only be 

 settled by tracing the development of the respiratory organs 

 of the Arachnida. Several authors have touched upon this 

 question. Thus Locy (1886) describes the later stages of 

 AgeJena ncevia as follows : — The lungs arise as a pair of 

 extensive invaginations. In sagittal sections they appear 

 as oblong plates of cells with the nuclei in parallel rows. 

 These nuclei are flattened 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- 

 lacuna3. Around each lamella is a chitinous membrane — the 

 ventral and the dorsal being continuous 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 tg^. 



A. T. Bruce (1886-87) 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. Kisliinouye (1890) states that in 

 the basal part of the first abdominal appendage there is an 

 ectodermic invagination, not deep or large. The wall of this 

 pocket which faces the distal end of the appendage is thicker 

 and its cells become arrranged 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 abdo- 

 minal appendage is another ectodermic invagination — a deeply 

 invaginated tube which remains in about the same state of 

 development until after hatching. The appendage shortens, 

 but is not invaginated. He believes it is very probable that 

 the lungs were'derived from the respiratory apparatus of some 

 Limulus-\\kQ aquatic form. He thinks that trachea) are 

 modified lungs. 



Laurie (1890), beginning with his stage K, describes the 

 changes in the abdominal segments of the Scorpion. At this 



