i893. ARACHNID AND INSECT DEVELOPMENT. 445 



Mr. Kingsley. Indeed, he considers it doubtful if the latter animals 

 should be regarded as arthropods, pointing out that their serial 

 nephridia, muscular pharynx, generally unstriated muscle-fibre, eyes, 

 and pre-oral antennae point to their relationship with the Chaetopod 

 worms. However, their reduced ccelome, heart and pericardium, 

 tracheae, and jaws will probably induce most naturalists to retain them 

 as primitive arthropods. 



While Mr. Kingsley has thus increased our knowledge of the 

 development of Limuhts, another American investigator, Dr. W. M. 

 Wheeler, has (6) made a valuable contribution to the embryology of 

 insects. His researches have been principally carried out upon a 

 species of Xiphidium, an orthopterous genus belonging to the family 

 of the long-horned grasshoppers (Phasgonuridae)." The females of these 

 insects lay their eggs in the galls produced on willows by midges 

 [Cecidomyia). The eggs of a grasshopper of a nearly related genus 

 (Orchelimum), a cricket (Gryllns), a "praying-insect" (Stagwomanfis), 

 and a marine collembolan (Annrida) were also studied. 



The process of gastrulation is described, and confirms 

 Cholodkowsky's researches on the cockroach and Graber's on 

 Stenobothviis in showing that this process in the Orthoptera corresponds 

 more closely than had been supposed with what occurs in the higher 

 groups of insects. A structure of great interest observed by Dr. 

 Wheeler in the development of the long-horned grasshoppers, is the 

 indusium. This organ, which seems not to have been before noticed 

 in the embryo of any winged insect, arises as a circular thickening of 

 the blastoderm in front of the head (Fig. 4). While the embryo moves 

 through the yolk, from the ventral to the dorsal aspect of the egg 

 (Fig. 5) the indusium increases in size until it has assumed a saddle- 

 shaped form, covering the greater part of the egg's surface (Fig. 6). 

 A layer, corresponding to the amnion of the embryo, is formed 

 within the serosa, over the indusium. Before hatching, the embryo 

 in its growth comes again to the original ventral aspect of the egg 

 (Fig. 7) absorbing the yolk, while the indusium becomes reduced to a 

 cap of cells at the apex of the egg. Dr. W^heeler considers the 

 indusium in these grasshoppers to represent the micropyle observed 

 in embryos of the Poduridae, and he gives a figure of the embryo of 

 Annrida (Fig. 8) to confirm this view. He would also compare the 

 structure with the dorsal organ of Crustacea, the primitive cumulus 

 of spider-embryos, and the embryonic sucking-disk of certain leeches. 



The antennae of the insect embryos examined are stated by Dr. 

 Wheeler to arise behind the mouth, and are so figured (Figs. 4, 8) 

 thus confirming Cholodkowsky's observations upon the cockroach.** 

 They are innervated from the deuto-cerebrum or first post-oral nerve- 

 mass. The segment of the trito-cerebrum (the ganglion next behind) 

 bears a pair of evanescent appendages in the embryo of Annrida 

 (Figs. 8, tc). With regard to the hindermost appendages of the 



"' Locustidac, auct. ** Nat. Sci., vol. i., p. 281. 



