554 SUMMARY OF CURRENT RESEARCHES RELATING TO 



a true reducing-division in Weismann's sense. In Ascaris megalocephala 

 bivalens the tetrads arise, not by a double longitudinal split of the 

 original spirem-thread, but by a folding of adjacent segments together 

 (conjugation of univalent chromosomes) along with what is believed to 

 be a single longitudinal split. The two split loops which form the two 

 tetrads appear very early in the continuous spirem, and in their later 

 development simply break apart, shorten, thicken, and straighten out till 

 the tetrads are formed. 



Since of each tetrad only one component chromosome remains in the 

 ripe ovum, there is a reducing-division in Weismann's sense, by which 

 paired chromosomes are -separated from each other in the egg, and the 

 hereditary characters transmitted by the chromosomes thereby modified. 



Anatomy of Nematodes.* — F. H. Stewart describes in some detail 

 the anatomy of Oncholaimus vulgaris Bast., a free-living Nematode, and 

 gives some notes on the reproductive system of Ascaris clavata and on 

 the excretory gland in the larva of an Ascaris from the cod. Of special 

 interest are the observations on the coelom. The cavities containing the 

 testes and ovary are true gonoccels or protocceloms. In the forms 

 described a series is made out. In the immature female or mature male 

 of 0. vulgaris there is a simple gonocoel ; next in the mature female the 

 gonoccel is slightly more complex ; there is a narrow conical outgrowth 

 from the original cavity, which is represented by the ovarian csecuin ; 

 finally in A. clavata the entire gonoccel has become enormously elongated 

 and convoluted. The call for this latter development is the need for an 

 enormous increase in the reproductive products on changing from a free 

 to a parasitic life. 



Platyhelminthes. 



Structure and Development of Cysticercus.f — H. Schaaf discusses,. 

 with particular reference to Tceuia solium, the structure and develop- 

 ment of cysticerci, of which he has had abundant material of different 

 ages. The cysticerci of T. serrata, T. saginata, and T. marginata are 

 also described. 



Echinoderma. 



Growth of the Oocyte in Antedon.f — Gr. C. Chubb has endeavoured 

 to interpret in terms of the cell-metabolism the structural changes 

 exhibited by the growing ovarian ovum of Antedon bifida Penant. 



Throughout the whole growth of the oocyte the nucleolus inter- 

 mittently discharges groups of deeply basophile spherules into the 

 cytoplasm. In the young oocyte these " nucleolar spherules " accumulate 

 in the cytoplasm, where they form small groups near the germinal 

 vesicle. In slightly older oocytes the increased fluidity of the cytoplasm 

 which results from the progressive accumulation of metaplastic material 

 in preparation for yolk-formation, causes the discharged nucleolar 

 substance to lose its spherular form, and to diffuse on the neighbouring 

 cytoplasm. The more deeply staining area of the cytoplasm to which 



* Quart. Journ. Micr. Sci., No. 197 (1906) pp. 101-50 (3 pis.). 

 + ZqoI. Jahrb., xxii. (1906) heft 3, pp. 435-76 (2 pis. and 13 figs.). 

 % Proc. Roy. Soc. London, Series B, lxxvii. No. B 519, pp. 384-7. 



