ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
305 
nephridia are true meta-nephridia, comparable to those of other coeloma- 
tous animals. As to the bearing of his results on the classification of 
the Polyzoa, the author would associate the Endoprocta with mesenchy- 
matous worms, on account of the absence of a true body-cavity and the 
nature of the nephridia, Phoronis with Sipunculids, on account of its 
nephridia and closed blood-vessels, and thus make the Ectoprocta alone 
constitute the Polyzoa. 
Arthropoda, 
a. Insecta. 
Effectiveness of a Net in excluding Insects.* * * § — Prof. F. Plateau, 
following Spence f (1834), has made a number of interesting experiments 
as to the effectiveness of a net in excluding insects, although the meshes 
were wide enough to allow their passage. Somewhat similar experiments, 
but less detailed, have been made by M. E. Pissot : J — 
Plateau’s conclusions are: — (1) A stretched net does not absolutely 
stop the flight of insects. (2) In their flight, the insects behave as if 
they did not see the meshes. (3) Direct passage during flight is always 
rare ; in most cases the insect stops and scrambles through, if at all. 
(4) The explanation is to be found in the lack of precision associated 
with compound eyes ; the threads of the net, like hatchings on an 
engraving, produce the illusion of a continuous closed surface. 
Relation of the Mimetic to the Original Form.§ — Dr. F. A. Dixey 
first gives a number of examples (figured) to show that the process of 
mimetic association depends rather on the development of old, than on the 
starting of new features, either of pattern or of colour. The series shows 
that, granted a beginning, however small, such as the basal red touches 
in the normal Pierines, an elaborate and practically perfect mimetic 
pattern may be evolved therefrom by simple and easy stages. Dr. Dixey 
discusses the question of the diversity of the two sexes as regards 
mimicry. The male is less mimetic, probably because its habits are 
different (Wallace), perhaps because the females select the more ancestral 
coloration (Belt), but the partial mimicry there is has probably its pro- 
tective value at certain times and on certain occasions. The author 
states some facts which suggest the occurrence of “ reciprocal mimicry ” 
— a kind of give-and-take arrangement, in consequence of which two or 
more inedible forms may hasten the assimilative process by imitating 
each other. Finally, he gives a case where the two extreme forms — 
Papilio and Heliconius — “ which by themselves might perhaps not be 
sufficiently near one another to be mutually protective to any very great 
extent, are held together, as it were, within the limits of an inedible 
mimetic group by the welding power of the intermediate Fwterpe-forms.” 
Post-Embryonic Development of Yasa deferentia and Accessory 
Organs in Male of Bombyx mori.|| — Messrs. E. Verson and E. Bisson 
call attention to the doubt which exists on the above subjects among 
entomologists, and give the results of their own investigations on this 
* Bull. Acad. Roy. Belg., xxx. (1895) pp. 281-302 (1 pi.). Cf La Natuialiste 
xi. (1889) p. 125. f Mag. Nat. Hist., vii. (1834). 
X La Naturaliste, xi. (1889) pp. 179-80, 202-3. 
§ Trans. Entom. Soc. London, 1896, pp. 65-79 (3 pis.). 
i| Zeitschr. f. wiss. Zoo)., lxi. (1896) pp. 318-37 (2 pis.). 
