DESCRIPTION OF TWO YOUNG TWIN HUMAN EMBRYOS WITH 17 



PAIRED SOMITES. 



Br James Crawford Watt. 



INTRODUCTION. 



The human embryos herein described are Embryos V and VI in the private collection 

 of Professor J. Playfair McMurrich. They were sent from Denver, Colorado, in 1908, by 

 Dr. Mary Hawes, who found them discharged by the uterus of a patient who had called 

 her during a miscarriage. They are specially valuable, as they occur midway in t he interval 

 between embryos of 13-14 paired somites and those of 22-23 paired somites described in 

 Keibel and Elze's Normentafel (1908). For the filling in of this large interval there has 

 hitherto been a great scarcity of material, so these embryos are described in detail, to serve 

 as an example of at least one stage in bridging the gap. 



The following facts are recorded concerning these embryos. The father was a ( ierman 

 Jew, 31 years old, tailor by occupation, and affected by tuberculosis for the last 5 years. 

 The mother was a German Jewess, 30 years old, robust and healthy, and had borne four 

 children previously, all living, the youngest being three years old and delicate in health. 

 Previous to this abortion the mother had experienced no trouble during her pregnancies. 



As regards this abortion, the last menstruation began on December 3, 1907, the flow- 

 being perfectly normal and lasting three days. Coitus first occurred after this on Decem- 

 ber 20, and the next menstruation did not appear on the expected date. Three days later, 

 however, on January 3, 1908, there occurred a slight bloody flow, followed by other similar 

 ones on the 11th, 12th, and 13th of the month, the intervals between these discharges being 

 entirely free. On the morning of January 14 there were three severe pains, followed in the 

 afternoon by hemorrhage, and ending in the night by the expulsion of twin sacs from the 

 uterus. 



PRESERVATION AND MOUNTING. 



These, sacs and their contents were, immediately after their extrusion from the uterus. 

 placed in 10 per cent formalin solution, followed by 70, 80, and 95 per cent alcohol. The 

 sacs were then cut away, except where the embryos were attached, and measurements and 

 drawings of each embryo were made. Each was then cut transversely into serial sections 

 10yu thick, which were stained on the slides with hemalum followed by erythrosin. Both 

 embryos, upon examination, appeared very similar in all features, so Embryo VI, which 

 was somewhat the clearer of the two, was selected for the most thorough study, the results 

 being supplemented by the findings in Embryo V. 



METHODS OF STUDY. 



By the aid of the camera lucida each section was carefully drawn at a magnification 

 of 200 diameters and from these drawings, following Born's wax-plate method of reconstruc- 

 tion, a model of the embryo was made. As there were 335 sections in the embryo, each 10/x 

 thick, the model measured 670 mm. or 27 inches long, each plate being 2 mm. thick. The 

 left side of the model shows the external appearance of the embryo, while on the right side 

 the skin and mesenchyme were not reconstructed, so giving a view of the internal structure. 



