EMBRYOLOGY 3G3 



off with a sheet of blotting paper. The melted wax is poured on 

 to the paper, and a heated metal roller, passing over the metal 

 gauge, leaves just the required amount of wax on tlic paper. The 

 latter easily peels off the surfaee of the stone. 



P'or more elaborate proeosses of plastic reconstruction (very compli- 

 cated and seldom necessary) see Born. " Die Plattenmodelliermethode," 

 in Arch. mik. Anat., 1883, p. 591, and Zeit. wiss. Mik., v, 1888, p. 433 ; 

 Sthasser, ibid., iii, 188G, p. 179, and iv, pp. 168 and 330 ; Kastschenko, 

 ibid., iv, 1887, pp. 235^6 and 353, and v, 1888, p. 173 ; Scuaper, ibid., 

 xiii, 1897, p. 446 ; Alexlvnder, ibid., p. 334, and xv, 1899, p. 446 ; 

 Peter, ibid., xxii, 1906, p. 530 ; Born and Peter, ibid., xv, 1, p. 31 ; 

 and Verh. Anat. Gcs., xiii, 1899, p. 134 ; Johnston, Anat. Anz., xvi, 

 1899, p. 261 ; FoL, Lehrb., p. 35 or j)reviotis editions ; Broman, Anat. 

 Hefle, xi, 1899, p. 557 ; Peter, " Die Methoden d. Rekonstruction " 

 (Fischer, Jena, 1906) ; Schonemann, Anat. Ilefte, xviii, 1901, p. 117 ; 

 Gage, Anat. Record, i, 1907, p. 167 ; Neumayer, Festschr. f. Kupffcr, 

 1899, p. 459 ; Mark, Proc. Amer. Acad. Sci., xiii, 1907, p. 629 (electric 

 wax-cutter for cutting out plates). 



Hill (Bull. Johns Hopkins Hosp., xvii, 1906, p. 114) finds that 

 embryos of mammalia taken from 95 per cent, alcohol and put into 

 caustic potash of 1 per cent, become so transparent that they can be 

 studied without cutting and reconstructinw. 



o' 



MAMMALIA 



801. Times for Early Development. The entry of the sperm 

 into the egg of the mouse takes place from six to ten hours after 

 copulation (Sobotta, Arch. mikr. Anat. Bd., 45). The pro-nuclei 

 stage of fertilisation is found from eighteen to twenty-two hours, 

 two-cell stage twenty-six hours, four-cell, fifty hours, eight-cell, 

 sixty hours after copulation : the egg remains in the tube about 

 eighty hours. J. A. Long and E. L. Mark {Contrib. Zool. Lab. 

 Museum, Harvard, Carneg. Inst. Wash., No. 142, 1911) find in the 

 mouse that ovarian eggs within fifteen or sixteen hours after 

 parturition have formed the first maturation spindle. Fertilised 

 eggs are obtained from animals killed between twenty-three and 

 thirty-one hours post partum. The time required for the sperma- 

 tozoa, after introduction into the uterus (either artificially or by 

 coitus) to reach the eggs in the first part of the oviduct varies 

 from four to seven hours in mice inseminated about the same 

 number of hours j^ost partum. To obtain free eggs for study, 

 Mark and Long kill mice fourteen to seventeen hours after 

 parturition, the ova being found in a fold of the oviduct. 



In the rat the eggs are found in the oviduct about 18-7 hours 

 and ovulation occurs in less than eighteen hours post partum. 



In the rabbit the pro-nuclei stage of fertilisation occurs about 

 fourteen hours, in the guinea-pig twenty-two to twenty-four 

 hours after copulation (Sobotta). The rabbit's egg, like that of 

 the guinea-pig, remains about eighty hours, the dog's egg eight 

 to ten days in the tube (Rothig, Embryol. Technik). 



