ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 57 



their mother-cells respectively, to the " spermatogemmfe " and 

 " spermatogouia " of La Valette St. George. 



Prof. Balbiani recognizes the cellular nature of the epithelial coat, 

 and inclines to believe that it results from a condensation of peripheral 

 cells of the sexual mass, rather than from a transformation of 

 surrounding embryonic cells. 



The chief results of this important and suggestive research may 

 be summed up in a sentence. The polar globules or cells, as yet 

 peculiar to Diptera, are the primitive sex cells ; they appear before 

 the blastoderm formation, at the posterior pole and at the expense of 

 the homogeneous plasmic layer ; after sinking into the vitellus, 

 reaching their ultimate position, and decreasiug in number, they 

 multiply endogenously, and almost the only noteworthy difference 

 between the male and female glands consists in the greater number and 

 smaller size of the nuclei and daughter-cells of the former. 



Prof. Balbiani indicates the relation of his researches to the 

 much debated subject of the origin of the generative organs. 

 Reviewing the various epochs of differentiation of reproductive cells 

 in the different groups, he shows how they might be thus chrono- 

 logically arranged, (a) Diptera and perhaps Aphides — sex-cells 

 formed first. (6) Daphnids — differentiated during segmentation, 

 (c) Chffitognatha — appearing in gastrula stage, and so on to vertebrates, 

 where they appear in an embryo already furnished with all its organs ; 

 while the climax of postponement is illustrated by those Hydroids 

 where they appear only in the completely developed, i. e. in the 

 Medusoid individual. Eeferring to Weismann's theory that the repro- 

 ductive cells are generally differentiated when the organism is otherwise 

 fit for reproduction, which is beautifully corroborated by the coin- 

 cidence of precocious appearance of generative cells and precocious 

 reproductive activity in Diptera, Daphnids, and Aphides, Balbiani notes 

 that Chironomus, though most strikingly illustrative of the former 

 characteristic, is divergent as regards the latter, since it remains 

 larval and without reproductive activity for several months. He also 

 notes the interesting relation of his researches to the theories of 

 heredity advanced by Nussbaum and Weismann, though refusing to 

 commit himself to any definite support of either. 



Histology and Embryology of Insects.* — M.H.Viallanes demon- 

 strates the existence of a subcutaneous nerve-plexus in many insects. 

 The hollow sensory hairs are each secreted by a modified hypodermic 

 cell, in whose protoplasm the prolongation of the nerve-cell ends. 

 The " dorsal vessel" is formed of a single layer of cells, but " each cell 

 is contractile through the presence in it of striated muscular fibrils," 

 each of which begins and ends in a small disc ; this condition verifies 

 the ordinary theory. The motor muscles of the wing differ from those 

 of the legs ; in the former there is no sarcolemma, and only a few 

 fibrils, but in the latter a sarcolemma encloses a single fibre. In 

 muscles consisting of one fibre, the nerve separates at once into its 

 constituent fibrils, whilst where the muscle consists of several fibres, 



* Amer. Natural., xix. (1885) p. 1001, from 'Rev. Scientifique.' 



