28 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
The higher Insects (Pterygota) have ancestors in common with the 
Thysannra, with which they were closely connected. The abdominal 
styles are not remains -of legs but secondary, paired, hairy structures 
which were at first purely sensory. The Collembola appear to be a 
direct side-branch of the Thysanura. All the Pterygota had the same 
origin. The ventral plates of the hind-body of the Hexapoda were 
derived from the fusion of the abdominal legs, developed in the embryo, 
with the whole ventral membrane, or with a median shield, which corre- 
sponds to the sternal shield of Myrio^^ods. 
Luminous Organ of Insects."^ — Dr. H. v. Wielowiejski has con- 
tinued his investigations on the luminous organs of insects, and com- 
mences with a criticism of the work of other observers. In Pyrophorus 
he finds that the ventral luminous plates consist of two layers. The 
upper, which is generally filled with crystalline concretions, agrees 
exactly in structure and relations with the “ urate layer ” of the Lamj^y- 
ridoe. But the special luminous plate is of a very different form to that 
which is typical of the just-named family ; the cells ajipear to be closely 
connected with one another ; their protoplasm is close and highly 
refractive ; on the surface there is a thickening which is not so well 
developed as in Lampyris italica. The rows of cells do not appear to 
be invested by a membrane of connective tissue, as Dubois supposes ; 
the small nuclei seen by the French observer belong to the tracheal 
capillaries which Dubois failed to see. The author cannot accejDt 
M. Dubois’s views as to the physiology of the luminous organs. 
Development of Insects. | — Prof. C. Emery reviews V. Graber’s 
researches J on the development of Insects. The abdominal appendages 
which occur in rej)resentatives of most of the orders were studied by 
Graber in Melolontlia, Eydrophilus, Mantis, &c., and are regarded as 
normal but rudimentary structures, the interpretation of which depends 
on the conclusions arrived at as to the ancestral forms. Both Graber 
and Emery incline to the opinion that the direct ancestors of insects 
were “ heteropodous,” and not “ homopodous.” Graber’s observations 
on the origin of segments in Steyiohothrus variahilis show that the seg- 
menting is not superficial, but that the hypoblast divides first into four 
“macrosomites,” and subsequently into “microsomites” or metameres, 
which agrees with what has been described in CEcantlms niveus by Ayers. 
Graber observes that the three thoracic segments in the hypoblast are 
difierentiated while the three segments of the mouth-appendages are 
still included in an undivided macrosomite. By hypoblast, Graber 
means the result of the invagination of the blastoderm, to the entire 
exclusion of the yolk-cells or “ centroblast,” to which he denies all share 
in forming the rudiments of the embryo. In reference to the enveloj^ing 
blastodermic fold (or “ gastroptyclie ”) Graber distinguishes the inner 
amniotic sheath as “ entoptygma,” the outer serous sheath as “ecto- 
ptygma.” Most of the insects investigated (e. g. Hymenoptera) show the 
typical process of folding, the yolk lying wholly on the dorsal surface 
* Zool. Anzeig:., xii. (1889) pp. 594-GOO. 
t Biol. Centralbl., ix. (1889) pp. 996-405. 
X INIorphol. Jabrb., xiii. pp. 58G-G15 (2 pis.); xiv. pp. 345 G7 (2 pis. and 4 ligs.). 
Deukschr. K. Akad. Wiss. Wien, liv. pp. 109-G2 (8 jds. and 2 figs.). 
