243 
The most striking result in following out the development of the 
villi of the human intestine is that they repeat all the stages found 
when they are studied from the standpoint of comparative anatomy !) 
In studying the development of the villi, the following questions 
were considered: 
1) The number of villi present in embryos of different ages. 
2) The forms of the villi in different stages, obtained by Born’s 
method of reconstruction. 
3) The form of the villi in different portions of the same intestine. 
In addition to the study of the development of the villi of the 
human intestine, I also studied those of the pig’s intestine. In these 
specimens the direct method of counting the villi was employed. The 
intestine was carefully removed from the embryo, cut open, and spread 
on a glass slide. First the area of the mucous surface was computed 
by careful measurement and then the number of villi in 0,01 sq. mm 
was obtained by counting the villi through a net measuring 0,1 mm 
on a side. Often camera drawings of all the villi within a given area 
were made. From all the measurements the average number of villi 
was obtained; and from it the number of villi in the entire intestine 
was estimated. The following table gives the result of these estimations: 
Table giving the Measurements of the Intestine with 
the Number of Villiin the Pig. | 
Length of Length of the Width of the Number of Villi Number of Villi 
the Embryo Small Inte- Small Inte- in one sq. mm in the whole 
in mm stine in mm stine in mm of Intestine Small Intestine 
62 240 3 48 33 760 
85 305 3 55 50 325 
136 795 4 ie, 228 960 
160 1050 7 64 470 400 
220 1850 9 69 1 148 850 
By the direct method of counting the villi, it is barely possible 
to obtain accurate results from embryo less than 60 mm long, and 
this matters little, for it is found from sections that the villi are not 
present in embryos much smaller. The results, however, are most 
definite, the villi increasing rapidly in number as the embryo grows 
1) After the present paper had been written there appeared the 
communication of Voier on the same subject in the Anatom. Hefte, 
Bd. 12, 1899. Voısr has followed the development of the villi in the 
pig’s intestine by means of reconstruction, and it is gratifying to me 
to be able to confirm his results. His work, however, takes into con- 
sideration more the villi of the intestine in the pig’s embryo while the 
present communication considers more the appearance of the villi 
throughout the human intestine. 
16* 
