No. 2.] THE EMBRYOLOGY OF LIMULUS. 225 



de la figure, et attachees en avant. Entre ces lamelles se 

 trouvent des cavites en forme de fentes qui communiquent en 

 arriere avec une cavite generale laquelle debouche a son tour 

 a I'exterieure par une fente stigmatique." 



Comparisons. — The only previous accounts of the gill de- 

 velopment are by myself ('85) and Kishinouye ('91, p. 72), and 

 the foregoing differs from them in being somewhat fuller in 

 some details (Kishinouye calls the metastoma an appendage^ 

 hence his appendage IX is my VIII, etc.). The process is ex- 

 tremely simple — the outgrowth of lamellate processes from 

 the posterior surfaces of the corresponding appendages, the 

 newer lamellae being formed proximally — and yet my early 

 account does not seem to have satisfied Laurie, who says ('91, 

 p. 137) "a detailed account of the development of these ap- 

 pendages Limulus may throw more light on the matter" of 

 the homologies of the respiratory organs of the scorpion and 

 the king crab. Had not Laurie been confused by some strange ^ 

 ideas of the homologies I think that my previous account 

 would have proved detailed enough for his purposes, for the 

 two organs, — the gill of Limulus and the lung of Scorpio, — 

 can be compared in detail in the simplest manner, without the 

 invocation of any inversion, of any " parabranchial stigmata," 

 of any conversion of air space into blood space, or the like. 



Several workers have described the development of the res- 

 piratory organs of the Arachnida, and from the papers of 

 Metschnikoff ('7l), Kowalevsky and Schulgin ('86), Locy ('86), 

 Bruce ('87), Kishinouye ('90), and Laurie ('90 and '92), we may 

 gain the following summary of the development of the lung 

 books in these forms. 



In these forms the lungs develop in connection with the ab- 

 dominal appendages. These appendages grow out for a short 



^ See upon this Kingsley ('85, p. 541, and '92, p. 60). 



2 Thus Laurie says (/.f. p. 136): " The additional appendages of Limulus are 

 directed towards the tail as one would expect abdominal appendages to be. Now 

 if the appendage had sunk without invagination, one would expect it to be still di- 

 rected towards the tail, unless there were some very good reason for its having 

 changed its direction. If, on the contrary, it had become invaginated it would 

 naturally be directed in the opposite direction towards the head, and this is what 

 we find in the scorpion. The inpushing is from the beginning towards the head, 

 and the aperture opens toward the tail." 



