II. 



The Development of Spiders' Lungs. 



I REGRET that, when compiling my " Further Notes upon the 

 Organs of Arachnids" (Natural Science, vol. v., pp. 361-5), I 

 overlooked an important recent memoir by M. Jaworowski, describing 

 the development of the breathing-organs in the large hunting-spider, 

 Trochosa signoriensis [Zeitschr. fur Wiss. Z00L, vol. lviii., 1894, PP* 54 - 78j 

 plate iii.) ; especially as the results obtained by this author seem to 

 contradict those of Mr. O. L. Simmons, whose work, as I mentioned, 

 supplied evidence for that view of the relationships of arachnid lungs 

 to tracheal tubes which I myself am disposed to accept. It will be 

 remembered that, according to Mr. Simmons' researches, the lung- 

 plates of spiders arise on the hinder surface of abdominal limbs 

 (comparable to the gill-bearing appendages of Limulus) which sink 

 into the abdomen as development proceeds. The tracheal tubes are 

 said to show at an early stage traces of pulmonary plates which after- 

 wards vanish. This, by itself, seems conclusive evidence that external 

 gills preceded lung-books, and that lung-books are more primitive than 

 tracheae. It is only right that the attention of the readers of Natural 

 Science should be called to M. Jaworowski's paper, which seems to 

 favour the opposite view. 



In the early stages of the development of the lung-books of 

 Trochosa, according to this observer, a tube runs dorsal-wards from the 

 in-pushing behind the abdominal appendage. This tube ramifies 

 into several branches, forming an embryonic tracheal system. As 

 the lung-book is developed, by the folding of the wall of the invagina- 

 tion, the tubes degenerate, the process beginning with the smaller 

 branches ; and, as growth proceeds, they disappear altogether. The 

 existence of similar vestigial tracheae has already been pointed out by 

 Professor Schimkewitsch in the embryo of Lycosa (Arch, de Biol., 

 vol. vi., 1887). 



From these considerations, M. Jaworowski concludes that among 

 the arachnids tracheal tubes must certainly have preceded lung-books. 

 He admits, however, the arachnid affinities of Limulus, and the 

 homology of the external gill-bearing limbs on the abdomen of that 

 animal with the lung-books, sunk within the abdomen, of a scorpion 

 or a spider. His conclusion, therefore, is in accordance with the 

 view of Dr. Simroth, as expressed in his book " Die Entstehung 



