362 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Diptera. — In Chironomus sp. the freshly laid ova show a con- 

 siderable contraction of the ytilk to have taken place ; a superficial 

 layer of protojilasm is also distinctly difFej-entiated. Before the 

 formation of aiiy traces of a blastoderm, masses of protoplasm, with 

 or without nuclei, become detached (usually at the anterior pole), and 

 subdivide, thus forming polar globules. Later are formed the polar 

 cells, a mass of twelve cells, at the posterior pole. The plasmatic 

 cortex is now occuj^ied by nuclei, and takes on a cellular character, 

 forming the blastoderm ; after this an anterior nucleus buries itself 

 in the vitellus, and there divides, as in Wiodites. 



Ortlwptem. — In Grylloialpa the ova are large, and there is no 

 plasmatic cortex. Cells composed of clear 2)rotopIasm are found in 

 the yolk soon after fertilization ; they make their way to the surface 

 and there divide, forming islands of smaller cells ; tliese islands 

 become connected together, and eventually form a continuous blasto- 

 derm. 



Three types of blastoderm formation are distinguished in the 

 above insects. 



1. Grijllotcdp)a. — Ova large ; cells apjpear in yolk and pass to the 

 surface. 



2. Rhodifes, Biorhiza. — Free nuclei pass to the surface and there 

 collect around them cell-bodies rich in nutritive yolk. 



3. CJiironomus. — The nuclei pass to the surface, to find there a 

 layer of protoplasm already dift'erentiated. 



4. The Poduridce present a fourth case. The small ovum forms a 

 blastodermic sac by total segmentation. 



It is noteworthy that the nuclei form no karyokinetic figures in the 

 process of division ; their amceboid movements have a purely nutritive 

 object ; the nuclei are not necessarily centres of attraction for proto- 

 plasm, for they remain for a considerable period independent of any 

 cellular bodies. 



Innervation of the Respiratory Mechanism in Insects.* — Dr. 0. 

 Langendorff denies Donhoff's statement that respiratory movements 

 in insects cease after decapitation. Experiments on humble-bees, 

 wasps, cockchafers, and dragon-flies, show that these movements con- 

 tinue in the abdomen after removal of the head, and even of the 

 thorax. Indeed, in some cases, sections of the abdomen of a dragon- 

 fly, as small as one ring and a half, continued the rhythmical respira- 

 tion. It is therefore evident that the nerve-centre for respiration is 

 not in the head. A decapitated cockchafer breathed for an hour. 

 Heat was found to increase the activity of respiration in mutilated as 

 in healthy individuals. Graphic illustrations are given of normal 

 respiration, and compared with those obtained from decapitated 

 specimens. 



Histology cf Insect Wing-muscles.t — G. V. Ciaccio finds that in 

 most insects the wing-muscles may be decomposed into fibrillfe (in 

 others, into striated fibres : Sphinx, Lihellula, &c.). In the former 



* Arch. Anat. u. Phys., 1883, p. 80. See Science, i. (1883) pp. 316-7. 

 t Arch. Ital. Biol., ii. (1882) p. 131. 



