46 SUMMARY OF CURRENT RESEARCHES RELATING TO 



be points out tliat it is impossible not to recognize that we have to do 

 with the generative organs of the animal, which have their origin in 

 the polar cells. From this mode of development flow some interest- 

 ing results with regard to the general morphology of the reproductive 

 organs. There is first their very early formation, preceding that of 

 all the other organs of the embryo, and indeed even that of the 

 embryo itself in its most rudimentary form, the blastoderm. There 

 is then the community of origin not only of the male and female 

 sexual products, but of those and of the embryo. We may therefore 

 say that the ovule, the spermatozoid, and the embryo have the fecun- 

 dated ovum as their common origin ; but whilst the latter is capable 

 of being directly developed, the two former only acquire the aptitude 

 for development by their reunion in a new fecundation. 



Embryonic Development of the Bombycini.* — The type chosen 

 by S. Selvatico to illustrate this subject is Bomhyx mori ; the ova of 

 Attaciis myliita and Saturnia pyri were also examined. The following 

 is the structure of the ovum at the end of winter : — (1) Solid globule, 

 attached to an opaque substance on its inner aspect. (2) Transparent 

 structureless membrane, considered by some as secreted by the blas- 

 toderm, but foimd by Tichomiroff before the appearance of the 

 blastoderm. (3) Serous envelope, consisting of large, flattened, 

 nucleated, polygonal cells containing pigment. (4) Nutritive yolk, 

 forming large spheres which contain one or more protoplasmic nuclei. 

 (5) Blastoderm, the ventral side turned outwards and covered by the 

 amnion. The amnion appears as a membrane with large nucleated 

 cells like those of the serous envelope, but without pigment. The 

 Malpighian vessels originate in the ectoderm. Selvatico was perhaps 

 prevented by the thickness or large size of the blastoderm in the 

 above Bombycini from noticing the early appearance of the rudiment 

 of the genital glands, which was observed by Balbiani in Tinea 

 crinella. 



Asymmetry of the Nervous System in Larvae.j — Anna K. 

 Dimmock, in dissecting a number of the larvae of Harpyia (Bomhyx) 

 vinula, found that the nervous system, instead of extending in a direct 

 line in the ventral region, as is common in insect larvae, curved out- 

 ward laterally between the first and second thoracic ganglia. This 

 curving, which was toward the left in six larvte examined, is to avoid 

 interference with the duct from a sac, or gland, which opens out 

 between the first and second thoracic ganglia. The gland secretes a 

 liquid, said to contain salicylic acid, which the larva ejects, as a 

 means of defence, when disturbed. The duct of this gland opens by 

 a transverse cleft, figured by Miiller,! on the ventral side of the first 

 segment posterior to the head. 



* BoUet. Bachicultura, viii. (1881) (7 pis.). Cf. Bull. Soc. Entomol. Ital., 

 xiv. pp. 250-1. 



t Psyche, iii. (1882) pp. .340-1 (1 fig.)- 



X O. F. Miiller, ' Pile-Larven med dobbc-lt Hale, og dens Phalaene,' 

 Kjobenhavn, 1772, pi. 2, fig. 3, d. Cf. also J. R. Rengger, ' Physiologische 

 Untersuchungen iiber die tliierischc Haushaltung dcr In.secten,' Tiibingon, 1817, 

 pp. 35-(j. 



