68 



amnion. The latter, of the size and form of a small grape, was ren- 

 dered quite tense by the liquor amnii, the transparency of its walls 

 permitting an accurate view of the entire contents. 



The embryo itself (PI. XIII., fig. I.) measured four lines in length 

 when fully extended, but in the curved form in which it lay when first 

 examined its length was only three lines and a quarter. Its utmost 

 weight, so far as I could estimate it, for it was impossible, without 

 destroying it, to remove the embryo from the fluid in which it was 

 examined, was one grain and a quarter.* Notwithstanding the ex- 

 tremely early period of development, many of the lineaments of the 

 future being could be distinctly traced ; the head (fig. II., 1), trunk 

 (2), rudimentary anterior and posterior extremities (3 and 4), and 

 some of the viscera, being clearly distinguishable. 



The head (fig. II., 1) in this specimen bears a less proportion 

 to the trunk than is observed in the second month of gestation. 

 The three masses of nervous matter constituting the three pairs of 

 ganglia for the corresponding sensual organs of smell, sight, and 

 hearing, are here of nearly equal size. The division between these 

 three pair of ganglia, the foundation of the future brain, is here very 

 well seen in viewing the object by transmitted light, a slight de- 

 pression at each point of junction also marking the divisions exter- 

 nally. The closest examination of the surface fails to detect any 

 sign of organs of sense, but a very careful observation by transmitted 

 light, with a good lens, discovers the eye (fig. II., 6), and ear (7) in 

 process of formation ; the earliest indications of these organs that I 

 have yet seen. The absence of any external indication of the eye 

 would alone ser^e to characterize the early stage of this embryo, 

 since, even in the early part of the second month, this organ is con- 

 spicuous from the deposit of pigment within it, which is then gene- 

 rally found. Transmitted light, however, exhibits the mere outline 

 of a slightly opaque, but well-marked circle, with a minute point in 

 its centre on either side of the head, lying immediately beneath the 

 second, or optic lobes, and just behind the first, or olfactory lobes, of 

 the primitive cerebral mass. 



A similar mode of examination detects another pair of minute 

 bodies (7), representing the acoustic vesicle or primitive internal 

 ears ; between the second or optic, and the third or auditory lobes, 

 or rather immediately beneath the latter. 



* T estimated the weight by cutting a piece of the fibrinous clot before mentioned 

 into the form and exact size of the embryo, and weighing this. 



