378 MINOT. [Vot. II. 
§ 12, Comparison with other rodents.— The history of the 
rabbit’s placenta elucidates also that of the Guinea pig, of which 
we possess descriptions by Bischoff, Ercolani, $9, Creighton, 
77a, 77b, Tafani, 134, and others. These authors being un- 
aware of the nature of the metamorphoses of the uterine glands, 
and not knowing the disappearance of the foetal ectoderm over 
the placenta, but, on the contrary, seeking for foetal placental 
villi, lacked the necessary basis for a correct interpretation. 
Ercolani was further misled by his erroneous belief that the pla- 
cental tissues of the mother arise as new formations, not as 
metamorphosed constituents of the uterine mucosa, but coming 
after the assumed but non-occurrent complete destruction of 
the mucosa. Tafani’s work betrays gross inaccuracy, for he 
based his figures and descriptions upon schematic notions, based 
in their turn upon very superficial, and often entirely false, ob- 
servations. To justify a judgment so severely unfavorable, it is 
necessary only to direct examination to some of Tafani’s plates. 
His drawings of the human placenta, for instance, /c. Tav. 
VII., leave a great deal to be desired; in Fig. 1 the sections of 
the villi are altogether too large and too few; the separate 
triangle of tissue at the edge of the placenta does not exist; the 
decidua is represented without any compact layer, and its gland 
cavities are made into blood-vessels. The section of the rabbit’s 
placenta (Fig. 2, Tav. IV.) is even more open to criticism, since 
it is impossible to determine the foundation of observation. 
Ercolani, on the other hand, was an observer of considerable 
ability, and his numerous memoirs on the placenta are valuable, 
although his hypothesis of xeoformaztone led him to adopt an 
unfortunate terminology which makes it difficult to follow him. 
Creighton observed with more impartial objectivity. That Bis- 
choff was a first-class observer every one knows; he never 
leaves any confusion between what he saw and what he in- 
ferred; for us he has the disadvantage of having written before 
the developments of recent histology. On the whole, we prob- 
ably do best to turn to Ercolani, who figures 89, Tav. IV., Fig. I., 
a section of a placenta of a Guinea pig near full term. Let us 
compare it with the rabbit’s placenta. 
It is discoidal, pedunculate, and bilobed. The upper surface is 
covered by a thin epithelium beneath which is a layer of vascu- 
lar connective tissue, Z, extending over the sides of the pla- 
