344 AIMEE S. VANNEMAN 



epithelium, soon migrating thence into the sex anlage. It will 

 be found interesting to use Swift's work on the chick as a basis 

 of comparison for the present paper on the Armadillo. For this 

 reason, Swift's conclusions are cited more or less in detail. 



Many other investigations might be cited in this connection, but 

 space and time do not permit of further enumeration. 



For the material of this investigation, I am indebted to Dr. 

 J. T. Patterson, who has generously furnished me with an 

 almost complete series. The embryos for the most part were 

 fixed in Bouin's fluid, and the sections stained in part in iron 

 haematoxylin, in part with Delafield's haematoxylin. In the 

 latter, the germ cells show up exceptionally well, as Delafield's 

 in coloring somatic cells relatively densely, permits the large, 

 clear germ cells to be easily distinguishable in their surroundings. 

 As most of the slides used for this work, had previously been pre- 

 pared for a purpose other than that of germ cell study, obviously 

 no selective technique could be employed for the present purpose. 

 However, unlike the experience of other investigators who have 

 studied the subject, I have found that whatever the stain or 

 fixing fluid used, the germ cells have been perfectly clear in the 

 tissues. The sections were cut from seven to ten micra thick. 

 It is to be regretted that the earlier stages were not cut thinner 

 as the germ cells of the earlier stages of development are not 

 grouped, but are few in number and often widely scattered and 

 for this reason, more difficult of detection and demonstration in 

 thick sections. 



The following are the stages examined for germ cells: (1) early 

 ectodermic vesicle stages, (2) early and late primary bud stages, 

 (3) secondary bud stages, (4) early and late primitive streak 

 stages, (5) three somite stage, (6) seven somite stage, (7) ten 

 somite stage, (8) fourteen somite stage, (9) 4-mm. embryo, 

 (10) 6-mm. embryo and (11) the 10-mm. embryo. Beyond the 

 10 mm. embryo, the germ cells are well established in the in- 

 different gonad, preparatory to undergoing further development. 

 The series is unusually complete, there being but one stage lack- 

 ing which would, if obtainable, be of value in tracing the germ 

 cells. This gap occurs between the 4- and 6-mm. embryo stages, 

 but is such that it can easily be bridged over. 



