I IO 



NEEDHAM. 



[VOL. I. 



and have been discussed as centers of replacement by Balbiani, 9 

 Bizzozzero, 10 and others. Throughout my work I have used 

 the term nidus as a convenient, descriptive, noncommittal 







name. 



Most of the recent investigators have looked upon them as 

 centers of regeneration, with various reasons for taking that 

 view. Van Gehuchten, finding the nucleus to be discharged 

 with the secretion, based his belief largely on the theory that 

 when a cell loses its nucleus it must die and be replaced. Bal- 



biani found nidi made up 

 of cells varying in num- 

 ber and size, and assumed 

 these to represent differ- 

 ent stages of development. 

 Bizzozzero and Cuenot at- 

 tach most significance to 

 the mitotic figures found 

 in the nidi and not found 

 elsewhere in the epithe- 

 lium, a fact noted by many 



l- lei. 8. The end of the discharge, x 220, from the . T., i 



same series as Figs. 6 and 7 , but from the anterior WritCFS. TlllS CVldcnCC IS 



end of the ventriculus. G, the last of the globules to crood SO far aS it 

 be thrown off ; these are nearly opposite the nidi. 



The mitotic figures indi- 



cate that cell division is in progress here, but tell nothing of 

 what may be doing elsewhere. It is now my privilege to add 

 as a result of experimental studies some additional evidence of 

 the correctness of the view that each nidus is a germinative 

 center. 



This evidence is based on observations upon (i) \\iesource of 

 the digestive secretion; (2) differentiation by reagents; (3) the 

 position of the nuclei ; (4) the decrease in the number of cells 

 in the nidi during digestion ; and (5) the encroachment of young 

 cells upon the old. 



(i) After tracing the discharge from beginning to end through 

 several series of experiments, it is perfectly evident that the 



9 BAI.BIANI, 1890: fitudes anatomiques et histologiques sur le tube digestif des 

 Cryptops, Arch, de Zool. Exp., xi. 



llj BIZZOZZERO, 1893: Ueber die Schlauchformigen Drusen, etc., Arch. Micr. 

 Anat., xlii. 



