TRANSITORY CAVITIES IN THE CORPUS STRIATUM. 101 



in these cells, although there is no indication of a constriction of the cell-body. An oddly 

 shaped nucleus has been pictured in figure 30 ; here the form is concavo-convex, with the 

 convex surface near the cell-membrane. This illustration is inadequate in so far as it gives 

 one the impression of a kidney-shaped nucleus. 



Unfortunately, not all of the material at my disposal has been exhausted in an effort 

 to establish a life-history for these macrophages. Many puzzling questions have been 

 presented by the distribution of the cells; yet a few general conclusions may be drawn from 

 these observations. With few exceptions, in the youngest human embryos the preservation 

 has precluded a careful cytological study; and often it is with reluctance that one admits 

 the failure to discover these cells in positions where one expects to find them. 



The chorionic villi in the very youngest ova seem to be devoid of the large vacuolated 

 cells first noted by Hofbauer. Embryos of 2 mm. (No. 391 in this collection) possess a few 

 of these cells sparsely scattered about the villi and a few in the chorion itself, but none in 

 the body stalk nor in the embryo. In the larger specimens parts of the villi are entirely 

 free from these independent cells, which are found in large numbers in other portions of 

 the villi, chorion, and even the body stalk (No. 186, 3.5 mm.; No. 164, 3.5 mm., and No. 

 463, 3.9 mm.), but the mesenchyme around the aorta or brain shows none of the typical 

 large vacuolated cells so common in the membranes. After the embryo has passed 5 mm. 

 these cells may be seen in the mediastinum and around the brain; the ease with which they 

 are found in the loose mesenchyme increases with the growth of the embryo. As noted 

 by Hofbauer, they gradually disappear from the villi as the mesenchyme takes on a more 

 fibrillar character. Hence in the older portions of the chorionic villi — i. e., those in which 

 the larger vessels and denser framework exist — relatively few of these phagocytic cells may 

 be found, even in the younger embryos. In the later stages they disappear from the pla- 

 centa entirely. 



Certain embryos contain a much larger number of macrophages in their placentae than 

 others of a similar stage of development. This peculiarity, as we shall see, holds true for 

 the cavities in the corpus striatum, where there is the same tendency to extreme variation 

 in the number of the cells present. The presence of large numbers of macrophages in one 

 locality is not necessarily accompanied by a similar increase in the other; thus in embryo 350 

 the placenta (fig. 14) contains very many cells, while the cavum mediale corporis striati con- 

 tains only a few (fig. 2) ; in embryo 22, on the other hand, the conditions are exactly reversed. 



In order to determine the origin of these cells more accurate methods of investigation 

 than the mere study of routine serial sections must be employed. Hofbauer's attention 

 was directed to their mode of origin by Marchand; these workers believed them to be 

 descendants of the connective-tissue elements. A section taken from embryo 800 might 

 be given in support of their view. The character of the cells of the layer of Langhans is not 

 very unlike that of the younger macrophages, and it is possible that the macrophages of the 

 villi may arise from that layer directly. The cells, when in the body of the embryo proper, 

 apparently preserve their specificity and give rise to younger generations by mitotic division. 



These cells, then, whose presence in the striate cavities argues strongly for the functional 

 existence of bilateral spaces, should be considered as of the type of extra-vascular phago- 

 cytes. They correspond in morphology to the Hofbauer cells of the young chorionic villus, 

 to the Wanderzellen of Maximow and Saxer, and to the macrophages of later writers. 



