The origin and histogenesis of the thymus in Raja batis. 459 



would appear to believe he established in fact in 1881 against the 

 divergent views of another writer. 



In this latter writing Stieda (1898) makes such remarkable 

 statements as to the actual results established in his former memoir, 

 that it may be of advantage to inquire as to what he wrote in 1881. 

 Like some of the classic memoirs of embryology Stieda's work of 

 1881 is often cited, but, apparently, seldom read. The writers of text- 

 books, who quote his "results", can never have read them, for had 

 they done so, it would have been seen, that the text-book accounts 

 were not in agreement with the original one. 



On the first page of the work the chief results are given in four 

 paragraphs, numbered 1—4. 



"1) Die Gl. thymus entwickelt sich, wie Kölliker richtig ver- 

 muthet hat^), aus dem Epithel einer Kiemen- oder Schlund- 

 spalte; sie ist demnach ein paarig angelegtes epitheli- 

 ales Organ." 



2) Relates to the thyroid. 



3) Relates to the Gl. carotica. 



"4) Weiter behaupte ich dann, dass die Reste der ursprünglichen 

 epithelialen Anlage der Gl. thymus in jenen bekannten ge- 

 schichteten HASSALL'schen Körperchen der Thymus zu suchen 

 sind; ich bestreite somit die Angabe Afanasjew's, wonach die 

 HASSALL'schen Körperchen nichts als obliterirte Blutgefässe sind." 

 These are all the results as given by Stieda, and while it is 

 asserted (behauptet), that the concentric corpuscles are products of 

 the remains of the original epithelial cells, nothing is stated as to 

 the fate of those epithelial cells, which do not go to form concentric 

 corpuscles. Moreover, in these results there is nothing as to the 

 origin of the lymphoid elements of the thymus. 



Following an account of the literature, his observations are given, 

 beginning with those on pig-embryos. The smallest such embryo dealt 

 with was 8 mm, the next 18 mm, and from this point the observations 

 are carried in the pig up to young pigs of 36 mm. What is esta- 

 blished in the pig is, that at first there is an epithelial thymus con- 

 nected with a gill-cleft. In the more abundant material of the sheep 



1) In Kölliker's original account the only "Vermuthung" mentioned 

 is, that prior to commencing his observations certain considerations led 

 him to suspect the thymus to be an epithelial organ. As the result 

 of his investigations the origin from an "umgewandelte Kiemenspalte" 

 is given as a proved fact. 



