III. 



Further Notes upon Arachnid and Insect 

 Development. 



TN an article in Natural Science (June, 1893) I gave a summary 

 -*■ of some recent memoirs upon the classification of arachnids 

 Mr. Goodrich has since (Natural Science, September, 1893) kindly 

 pointed out that the views of Mr. Pocock on the relationships of the 

 arachnid orders, therein set forth, agree in the main with those put 

 forward twelve years ago by Professor Ray Lankester (i), in his 

 memoir advocating the arachnid affinities of the King-Crab. 



Ever since the appearance of that well-known paper by Professor 

 Lankester, Limulus has been an animal of exceptional interest to 

 zoologists. The recent publication by Mr. Kingsley (2) of a detailed 

 description of the embryology of the King-Crab is therefore worthy of 

 special notice. His results, on the whole, strongly support the 

 arachnid affinities of Ln/ni/»s; its development is shown to have but 

 little correspondence with that of Crustaceans. 



The structure of the ovary resembles that of scorpions, spiders, 

 and mites. The ova are developed from the columnar epithelium of 

 the ovarian tubes, and pass into a space between the epithelium and 

 the tunica, which, at first, are in contact with each other. The 

 segmentation of the egg proceeds by delamination, similar to that 

 observed in various spiders, harvestmen, and mites. The mesoderm 

 arises by proliferation from the thickened region of the blastoderm, 

 and ccelomic cavities are formed in the somites by the splitting of the 

 mesoderm into two sheets. The body-cavity of the adult is, however, 

 due to secondary spaces in the mesodermal tissues. Each ccelomic 

 cavity becomes divided into a dorsal and a ventral part ; the former 

 is believed to give rise to the generative glands; the latter is lost in 

 most of the somites, but in the fifth it develops into the coxal gland 

 (nephridium). This corresponds with the fate of the coelome and the 

 origin of nephridia in Pevipatus and in arthropods generally ; ' it 

 specially recalls the origin of the coxal glands in arachnids.- The 

 formation of the alimentary tract agrees with what occurs in 

 arachnids, and contrasts with the corresponding process in crustaceans, 

 for, while the stomoda^um is long, the proctodaium is short, and late 

 in its appearance. Mr. Kingsley states that his results are, in the 

 main, confirmed by the researches of Mr. Kishinouye (3) upon the 

 development oi Limulus longispina. 



^ Nat. Science, vol. i., p. 282. -Ibid., pp. 524, 525. 



