290 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Arthropoda. 

 a. Insecta. 



Variation in Head-length of Spermatozoa in Insects.* — C. Zeleny 

 and C. T. Ijenay have investigated head-length of spermatozoa in seven 

 additional species of insects, bringing the number studied up to twenty- 

 two species. The new data on the whole substantiate the view that 

 dimorphism in size of spermatozoa is of common occurrence in those 

 groups of animals in which two chromosomal classes of spermatids are 

 frequent. In both the Hemiptera and Coleoptera a great majority of 

 the species studied show a quantitative difference in chromosomal 

 content among the spermatids, though in each case there are some 

 species which show no difference, or only a slight one. " The chromo- 

 somal dimorphism of spermatogenesis is represented in the active 

 functional spermatozoa by size-dimorphism. Control of sex, then, 

 merely awaits our ability to separate the two sizes in the living condition 

 and to use them in artificial insemination." 



Early Stages of Development in Some Hymenopterous Parasites. f 

 F. Silvestri has studied the structure of the egg and the early stages of 

 development in five Chalcididge. In Encyrtus mayri, whose ovum is 

 deposited in the ovum of the Lepidopterous species, (EcophjUemhms 

 neglectus, the structure of the ovum, the maturation, and the fertiliza- 

 tion agree with what Silvestri has previously described in Litomastix, 

 Ageniaspis, and Copidosoma, and the polar bodies behave as in Ageiiiaspis 

 and Copidosoma • the polar part of the ovum does not enclose the 

 embryonic cells until the fourth segmentation, thus much later than in 

 Ageniaspis ; one of the first four cleavage cells differentiates into a 

 germinal cell as in Litomastix and Copidosoma ; the development in this 

 species is mono-embryonic ; the embryo is never surrounded by a true 

 cyst of its host, but merely by the tissues and cells of its host, which 

 remain unaltered in character. No chromatin-elimination process was 

 observed in the maturation division or later. 



In Encarsia partenopea the egg is laid in the body of a young repre- 

 sentative of the genus Aleyrodes. The activity of the polar globules 

 ends at the third segmentation, after which they exhibit involution, 

 taking no part in the development of the embryo. The posterior pole 

 of the Qgg, in which the germinal cells are differentiated, is rather con- 

 stricted off. The differentiation of the first germinal cells begins at 

 the stage when there are eight segmentation-nuclei. 



In ProspateUa (Doleresia) conjugata the egg is also laid in the body 

 of a representative of the genus Aleyrodes. The structure of the egg and 

 early stages of development are as in Encarsia, but the polar globules 

 have no marked period of activity, and the first germinal cell is marked 

 at the fifth division instead of at the third. 



In ProspateUa herlesi, the egg of which is laid in the body of the 

 female of JDiaspis pentagona, there is no distinct " oosome " (a granular 



* Journ. Exper. Zool., xix. (1915) pp. 505-12 (8 figs.). 



t Boll. Lab. Zool. Scuola Agric. Portici, x. (1915) pp. 66-88 (6 pis. and 4 figs.). 



