ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 583 



spermatocyte chromosomes. As the ovum passes down the oviduct a 

 second nuclear membrane is formed, enclosing a much smaller area than 

 did the former nuclear membrane before the biserial arrangement. No 

 typical metaphase figure is ever formed, the chromosome pairs in the 

 biserial arrangement, passing directly into anaphase and telophase. 

 The relative size of the chromosomes remains constant throughout the 

 different stages of segmentation. Both egg-maturation spindles are 

 entirely within a nuclear membrane. The spindle-fibres, attached sub- 

 terminally or medially to the chromosomes, appear most distinctly in the 

 second maturation spindle. The spindle-poles are very broad, so that 

 the fibres appear to run almost parallel to one another. The chromo- 

 somes in one of the two contiguous pronuclei are already splitting, 

 preparatory to the first segmentation-division, before the formation of 

 spindle-fibres. The four American " varieties " of Cyclops viridis ex- 

 hibit a constant difference in chromosome number. C. viridis (type sp.) has 

 twelve, var. 6f???^/c«/z?/s has ten, var. j?«^rc?<s has six, and var. hrevispinosus 

 has four chromosomes. The six chromosomes of C. parens are in three; 

 sizes, there being a pair of each size. The chromosomes of a pair do not 

 necessarily lie together in the spermatogonial or oogonial nucleus. 



With regard to spermatogenesis in C. americmius, the investigator 

 finds that in a mature individual a " Keimpolster " distinct from the 

 adult testis may exist. Nuclei in synizesis are smaller if anything than 

 the last spermatogonial nuclei. In the testis synizesis is accompanied by 

 only a very slight growth. The nucleus in synizesis resolves itself into 

 five pachytene filaments, from each of which develop two filaments 

 spirally coiled about one another. The five double filaments uncoil, 

 and become the five paired chromosomes of the spermatocyte nucleus. 

 The single elements of the double spermatocyte chromosomes are elon- 

 gate, dumb-bell shaped, similar to those of the oocyte. The spermatid 

 chromosomes resolve into a hollow sphere of reticular chromatin. 

 The ripe spermatozoon consists of a spermatid nucleus drawn out into a 

 slightly spiral spindle-shaped body with fine tapering ends. 



Panama Copepods.* — C. Dwight Marsh describes some new species 

 from the Canal zone, and discusses the distribution of others. Some 

 species are cosmopolitan, and are therefore of no special significance. 

 The general character of the Copepod fauna of the Canal zone is 

 much more closely related to the South American fauna than to that of 

 North America. Some species are common to the Atlantic and Pacific 

 slopes ; some are confined to one slope or the other. 



New Genus of Parasitic Copepods. t — H. Leighton Kesteven de- 

 scribes Ubius hilli g. et sp. n., a minute parasite from the genital ridges of 

 Ptychodera austrcdis, which occurs near Port Jackson. The new form is 

 closely allied to the monotypical genus Ive Mayer, but differs in having 

 a paired ovary, no chitin-lined end-gut, and a much reduced nervous 

 system. The body shows no trace of segmentation ; there are five pairs 



* Smithsonian Misc. CoU., Ixi. (1913) No. 3, pp. 1-30 (5 pis.), 

 t Proc. Linn. Soc. N.S.W., xxxvii. (1913) pp. 673-88 (3 pis.). 



