Microscopical Society. 2785 



The entire ovum weighed 6 drachms, and measured 2 inches in length, and \\ inch 

 in its shorter diameter ; all the membranes were entire and perfectly distinct from 

 each other. The embryo itself measured only 4 lines in length, and notwithstanding 

 the extremely early period of development, the lineaments of the future being could 

 still be distinctly traced. The head, trunk, anterior and posterior extremities, 

 and some of the viscera being clearly distinguished. The head bears a less propor- 

 tion 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 of nearly equal size. The division between 

 these three pairs of ganglia, the foundation of the future brain, are here very well seen 

 on viewing the object by transmitted light. The closest examination of the surface 

 fails in detecting any signs of organs of sense, but a very careful examination by 

 transmitted light, with a good lens, discovers the eye and ear in process of formation, 

 being the earliest indication of these organs ever seen by Dr. Farre ; and although 

 no external signs of these organs can be perceived, the appearance of a slightly opaque, 

 but well-marked circle, with a minute point in its centre on either side of the head, 

 being the rudiments of the eyes, and another pair of minute bodies representing the 

 internal ears are clearly distinguishable, although there exists no outward indication of 

 their presence ; and thus it is seen that the head, at that early period, consists of three 

 primitive pairs of cerebral ganglia, arranged in a triangular form, with traces of the 

 organs of vision and hearing, the whole being invested in a soft, white integument. 

 Immediately below the head, the body forms a gently curved line in which, by transmit- 

 ted light, parallel lines at regular short intervals are seen, indicating the future vertebral 

 column and its divisions, which are as yet equal throughout its whole length, which line, 

 after curving somewhat abruptly forward at its extremity, ends in a narrow point or tail. 

 On either side of the trunk are minute projections, indicating the future extremities : 

 the anterior are more developed than the posterior pair, and are about one-third of a 

 line in length ; the latter are situated closely on either side of the pointed extremity of 

 the trunk, and are thus rendered less conspicuous than the upper pair. The whole 

 anterior part of the body is perfectly open, from the head to the point of origin of the 

 umbilical vessels. The mouth and nose are not as yet formed, but indications of the 

 commencing formation of the naso-buccal fissure, which itself is again transformed 

 into those organs, are present. The only viscera which can be discovered, are a small 

 mass on the right side, indicating the future liver ; and on the left side, at the same 

 height, a curved vessel or hollow organ, divided into three parts, indicating the 

 future heart. With the exception of the organs just mentioned, no others appear to be 

 as yet formed ; slight traces which may be indications of the primordial kidneys, &c., 

 are, however, visible. Immediately above the curved extremity of the trunk, the mi- 

 nute umbilical cord is seen, blending itself with the chorion and surrounded by the 

 amnion, but the course of the vessels cannot be traced. No indications of the presence 

 either of an umbilical vesicle or of an allantois can be perceived in this embryo. In 

 referring again to the heart, Dr. Farre described it as presenting the appearance of an 

 elongated vessel curved upon itself, and exhibiting three divisions or chambers, repre- 

 senting the single auricle, ventricle, and bulbus arteriosus, which compose the heart of 

 the lowest class of vertebrate animals or that of fishes ; and, in order to carry out the 

 analogy, two drawings of the heart in the human foetus in successive stages of develop- 

 ment, the one at the beginning and the other at the end of the second month, were ex- 

 hibited, the first representing it as composed of two auricles and but one ventricle, thus 

 symbolizing the heart of vertebrate animals next in advance of fishes, viz., reptiles. 



