234 Henry Fox 



in which I examined a large series of relatively late foetal stages the 

 follicles as late as the twenty-first day maintained the same histological 

 character, that is, they were composed of small-celled epithelial tissue. 

 The latter, however, bears a strong resemblance to ordinary lymphoid 

 tissue, and its persistence at this late period in this animal suggests 

 that the fundamental tissue of the definitive thymus may be really 

 epithelial and not lymphoid tissue. Such a view has recently been 

 supported by Stohr. On page 9 of his article "Ueber die Thymus" (Sitz- 

 ungs-Berichte der physikalisch-medicinischen Gesellschaft zu Wiirzburg) 

 he writes, "Die Thymus ist ein epitheliales Organ von Anfang his zu 

 Ende, so gut wie etwa sine Speicheldriise." My own observations do 

 not cover sufficiently late stages to enable me to give any strong support 

 to this view. 



Regarding the origin and structure of the carotid gland there has 

 been considerable diversity of opinion. Steida first described the organ 

 and postulated its origin from the endoderm. This view was later sup- 

 ported by Fischelis, Kastschenko, on the other hand, makes no distinc- 

 tion between the carotid gland and the associated dorsal extremity of the 

 thymus, both of which are included in his nodulus thymicus. The latter 

 he regards as simply the much swollen dorsal end of the thymus. He 

 apparently overlooks the vesicular structure of the gland — an oversight 

 which is not surprising when one bears in mind that this structure is only 

 shown in sections suitably double-stained. 



Steida, while correct in his derivation of the gland from the endo- 

 derm, errs when he states that it later separates from the thymus anlage 

 and comes into contact with the carotid artery. Kastschenko maintains 

 that the nodulus thymicus, with which he considers the carotid gland of 

 Steida to correspond, never separates from the thymus. He shows that 

 the body which Steida took for the gland in later stages is of an entirely 

 different character. It forms ein verldngerter ellipsoider Knoien, which 

 surrounds the internal carotid at the bifurcation of the common arfery. 

 This he maintains is merely a local thickening of the adventitia of the 

 artery. 



My observations show that the contention of Kastschenko is correct. 

 The carotid gland does not separate from the thymus, at least not in 

 any stages examined by the two investigators mentioned. I find the 

 same peculiar thickening of the adventitia of the internal carotid artery 

 as described by Kastschenko in both the pig and cat. It is particularly 

 large and prominent in pigs of 17-24 mm. and cats of 23-31 mm. In 



