ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 577 



by the oocytes. The oocytes pass through synapsis, out of which come 

 long beaded threads ; these break up, the contained chromatin-granules 

 remaining together in small achromatiu masses. 



Development of Ovary of Phryganid.* — W. S. Marshall has studied 

 Platyphylax designatus Walk, as regards the development of the ovary, 

 tracing the history from homogeneity to the differentiated oocytes. 



Development of Gonads of Tenebrio molitor. f — Th. Saling has 



followed the development in both sexes, starting from the extremely 

 similar ovarian and testicular primordia, and working onwards to the 

 differentiated organs. 



■"to"- 



Spermatogenesis of Hornet.! — F. Meves and J. Duesberg have 

 studied in particular the spermatocyte divisions of Vespa crabro, and 

 find that the first division is practically the same as in the bee, including 

 the formation of non-nucleated directive corpuscles. In regard to the 

 bee, Meves has suggested that the nuclear division in the first spermato- 

 cyte division is suppressed because the drone develops from an unfertilised 

 ovum which forms two polar bodies. All the cells derived from such 

 an ovum should have reduced nuclei. The suppression of the nuclear 

 division in the first spermatocyte division prevents further reduction of 

 chromatin-mass and number of chromosomes. It is suggested that the 

 males of wasps and ants are developed from unfertilised ova. 



Spermatogenesis in Insects. — H. Otte§ gives a detailed account of 

 the spermatogenesis in Locusta viridissima ; the spermatogonium has 

 16 pairs of chromosomes ; the spermatozoon has 16 ordinary chromo- 

 somes (each probably half maternal and half paternal) ; in half of the 

 spermatozoa there is an accessory chromosome. 



G. Wilke || gives an account of the spermatogonia, tetrad-formation, 

 and two maturation - divisions in Hydrometra lacustris, one of the 

 Hemiptera. 



W. D. Henderson 1[ has studied the spermatogenesis of Dytiscus 

 marginalis, and has followed the changes of the chromosomes from the 

 spermatogonia to the end of the second maturation division, his results 

 agreeing in the main with those of A. and K. E. Schreiner. 



Friedrich Schafer ** has made a detailed study of the spermato- 

 genesis of Dytiscus, with special reference to the chromatiii-reduction. 

 In the spermatogonia there are 36 normal and 2 accessory chromosomes ; 

 the reduction in number occurs in the synapsis stage of the spermato- 

 cytes by apposition and conjugation of two homologous chromosomes. 

 In the metaphase of the first and second maturation-division, there are 

 18 normal bivalent chromosomes, plus one accessory chromosome. There 

 as no reduction-division in Weismann's sense ; both maturation-divisions 



* Zeitschr. wiss. Zool. lxviii. (1907) pp. 214-37 (2 pis.). 



T Tom. cit., pp. 238-303 (2 pis. and 14 figs.). 



J Arch. Mikr. Anat., lxxi. (1908) pp. 571-87 (2 pis.). 



§ Zool. Jahrb., xxiv. (1907) pp. 431-520 (3 pis. and 2 figs.). 



j| Jen. Zeitschr. f. Naturw., xlii. (1907) pp. 669-720 (3 pis. and 19 figs.). 



^ Zeitschr. wiss. Zool., lxxxvii. (1907) pp. 644-84 (2 pis. and 5 figs.). 



** Zool. Jahrb., xxiii. (1907) pp. 535-86 (1 pi. and 7 figs.). 



'Oct. 21st, 1008 2 Q 



