318 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Accessory Chromosome in Aplopus mayeri.* — H. E. Jordan traces 

 the history of the accessory chromosome in the Phasmid, Aplopus mayeri, 



from its first origin in the secondary spermatogonia, through its various 

 changes during the growth and maturation processes, to its final disappear- 

 ance in thr head of the ripening spermatozoa. He reserves theoretical 

 considerations for future discussion, and summarises the results of his 

 investigation as follows. The accessory chromosome appears in the 

 resting stage of the secondary spermatogonia as a chromatin nucleus 

 characteristically close to the nuclear wall. At the last spermatogonia] 

 division it passes over into the resting stage of the primary spermatocyte 

 without entering a reticular stage, as do the ordinary chromosomes. 

 Both the primary and secondary spermatogonia have a metaphase group 

 of thirty-five chromosomes. Metaphase groups of the follicle cells of 

 the ovary contain thirty-six chromosomes. Synapsis occurs in the early 

 stages of the growth period by an end-to-end union of pairs of univalent 

 elements. Equatorial plates of primary spermatocytes contain eighteen 

 chromosomes. The accessory chromosome passes undivided to one pole 

 of the first maturation spindle, and thus produces a dimorphism of the 

 daughter-cells and the resulting spermatozoa. The first maturation 

 division is reductional, the second is equational. Equatorial plates of 

 secondary spermatocytes show a disparity in the number of chromosomes ; 

 one group contains a large U-shaped element peripherally and numbers 

 eighteen ; those groups which lack a body of such form contain only 

 seventeen chromosomes. The accessory chromosome can be traced as a 

 specific structure from the resting stage of the last order of spermato- 

 gonia through all the various phases of synapsis and maturation, until 

 it disintegrates in the head of the ripening spermatozoon. 



Excretion in Thysanura.f — L. Bruntz finds labial renal organs 

 opening to the exterior in MacMlis and Lepisma. There are also nephro- 

 cytes like fat^cells in the connective-tissue which bounds the pericardial 

 sinus in MacMlis. Similar elements in Lepisma, but quite unlike fat- 

 cells, occur in connection with the pericardial sinus. Phagocytosis is 

 exhibited by blood-corpuscles and by the pericardial septum in some 

 species {Lepisma saccharin a and Ctenolepisma lineata). 



P, Myriopoda. 



Habits and Structure of Scutigerella immaculata.J — S. R. 

 Williams has studied this member of the Symphyla, that interesting 

 group of Arthropods that seems to partake to a certain extent of the 

 characters of the millipedes, the centipedes, and the Thysanuran order 

 of insects. It lays eggs and hatches its young (in the latitude of 

 southern Ohio) during late May and early June. The time of laying is 

 influenced by the temperature. In the laboratory at least the adult is 

 needed to keep off destructive fungi from the eggs. The egg is covered 

 by a vitelline membrane and a much-ridged chorion. 



The larva has seven pairs of legs and ten dorsal scutes, and is 



* Anat. Anzeig., xxxii. (1908) pp. 284-95 (35 figs.). 

 t C.R. Soc. Biol. Paris, lxiv. (190S) pp. 231-3. 



Proc. Boston Soc. Nat. Hist., xxxiii. (1907) pp. 461-85 (3 pis.). 



