ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 783 



presenting dimensions regularly decreasing to tlie thirty-eighth 

 somite, which measures merely 37 /a in diameter. This fact is not 

 teratological, but is fully confirmed by various other embryos, all 

 perfectly normal, but slightly differing in age. 



With the exception of the last two, all the caudal vertebrfe have a 

 blasteme of cartilaginous substance, similar, except in size, to that of 

 every other vertebra of the series. The last two are only indicated 

 by myomeres, perfectly distinct from the rest. The extremity of the 

 tail is formed by the termination of the medullary tube, covered 

 merely by the skin. The dorsal cord extends, therefore, quite close 

 to this extremity. 



The last caudal vertebrfe have but a very ephemeral existence. 

 Already in embryos of 12 mm., that is to say, of six weeks, the 

 thirty-eighth, thirty-seventh, and thirty-sixth vertebrae are blended 

 together into a single mass, and the thirty-fifth itself has no longer 

 very distinct limits. An embryo of 19 mm. has merely thirty-four 

 vertebras, the thirty-fourth resulting from the fusion of the four last. 

 At this moment the tail altogether is already much less prominent. 



It results from these facts that the human embryo during the fifth 

 and sixth week of its development is furnished with an incontestable 

 tail, regularly conical, elongated, and deserving the name in all 

 respects. It is deprived of all physiological utility, and must rank 

 among the rudimentary organs.* 



Nature of the Placental Neoformation and ithe Unity of Com- 

 position of the Placenta.j — M. Laulanie discusses the two types of 

 placenta and Ercolani's attempt to reduce these two types to one — the 

 multiple — on account of a constant secretory epithelium. He con- 

 cludes that in all cases the maternal neoformation of the placenta is 

 the result of a conjunctivo-vascular process, and that the maternal 

 surfaces are invariably destitute of the secretory epithelium which 

 Ercolani has attributed to them. 



Foetus of Gibbon and its Placenta.| — M. J. Deniker describes 

 the foetus of a species of gibbon (either Hilohates lar Saint-Hil. or 

 H. agilis F. Cuv.) and its placenta, and points out that the placenta of 

 the anthropoid apes is single, the double placenta being only met 

 with in these animals by way of exception, as in the human race and 

 in certain genera of monkeys, c. g. Hapale. 



Spermatogenesis in the Rat.§ — Mr. H. H. Brown finds that the 

 rat is an advantageous animal f(jr the study of spermatogenesis, owing 

 to the large size of its spermatozoa. 



The research was conducted by means of sections and by teasing ; 

 the history of the nuclei was made out with sections prepared by the 

 paraffin-shellac method and by staining with ha^matoxylin ; sections 

 stained in chloride of gold solution showed jiarticularly the proto- 

 plasmic structures and the outlines of the cells, while the nuclei, 



♦ Sec Joum. of Rci., vii. (1885) pp. 416-9. 



t CVnnptcH R(;ti<lu8, c. (1885) pp. 651-3. 



; Iljiil., pp. 651-6. 



§ Quart. Journ. Micr. Bci., xxv. (1885) pp. 313-6'J (2 pis.). 



