592 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
the nutritive cells being included in each follicle with the ovum, just 
above it or distal to it. The ovariole is almost exactly similar to that 
of Musca. The oviducts are very highly modified from the typical con- 
dition. At the anterior end of the uterus the dorsal surface is pierced 
by an opening, through which enters the nutritive secretion of the two 
pairs of milk-glands. The whole system is described in detail. 
Instinct and Tropism in Insects.* — Mr. W. M. Wheeler points out 
that in the hovering of many insects, the insects adopt positions having 
fixed relations to the air currents. To this phenomenon he gives the 
name of anemotropism, this being positive or negative according to the 
position of the insect’s head relative to the direction of the wind. This 
anemotropism is, according to the author, only a particular form of rheo- 
tropism, or the response which organisms make to the conditions to 
which their existence in a fluid medium exposes them. He believes 
that most of the responses to environment displayed by organisms are 
mere reflexes, and that the so-called instincts are mostly as purely 
mechanical in origin as the movements of Mimosa leaves after a sudden 
blow. They are due to the various tropisms, and the psychical factor 
is introduced needlessly. 
Flowers and Insects-! — In his latest paper on this subject, Mr. C. 
Robertson discusses the following questions: — (1) Comparison of the 
g< nera of bees observed in Central Germany and in Illinois, with the 
number of species of each and their flower-visits ; (2) The flower-visits 
of oligotropic bees; (3) Competition of flowers for the visits of bees; 
(4) The influence of bees in the modification of flowers ; (5) The sup- 
posed pollen-carrying apparatus of flies and birds. He rejects, as fatal 
to the theory of natural selection, the hypothesis that, on the head of 
the ruby-throated humming-bird are feathers which are specially modi- 
fied for carrying pollen. 
Development of Lepidoptera.! — Dr. Erich Schwartze has under- 
taken the investigation of the origin of the mid-gut in Lepidoptera, 
in the hope of settling the dispute as to the cells from which it arises. 
Three positions have been held on the subject, — (1) that it originates 
from the yolk-cells; (2) from anterior and posterior endodermic pri- 
mordia which are separated from the endomesoderm soon after the 
origin of the latter from the ectoderm ; (3) that it together with the re- 
mainder of the gut arises from the ectoderm. The author’s investigations 
point conclusively to the last position. He finds that fore-gut and hind- 
gut arise from ectodermic invaginations, and from these invaginations 
lateral lamellae arise which grow towards one another, and ultimately 
fuse together and form the mid-gut. Save for its mesodermal muscu- 
laris the mid-gut is therefore as purely ectodermal in origin as stomo- 
daeum and proctodeum. The yolk-cells separate themselves from the 
other cells before the formation of the blastoderm, and remain lying 
within the yolk without receiving any increase in number from cells 
migrating from the blastoderm. Certain cells (paracytes) do migrate 
* Arch. f. Entwick.-mech., vii. (1899) pp. 374-81. See Zool. Centralbl., vi. 
(1899) pp. 695-7. 
t Bot. Gazette, xxviii. (1899) pp. 27-45. Cf. this Journal, 1898, p. 445. 
X Zeitschr. f. wiss. Zool., lxvi. (1899) pp. 450-96 (4 pis.). 
