THE FORMATION OF PROGLOTTIDS IN CROSSO- 

 BOTHRIUM LACINIATUM (LINTON). 



WINTERTON C. CURTIS. 



I. INTRODUCTION AND SUMMARY. 



The statement that all cestodes form their proglottids by the 

 insertion of each new one between the scolex and the one last 

 formed, has been current in our text-books for years and so far 

 as I know there are no statements to indicate that any other 

 mode of origin ever occurs. Upon turning to the original liter- 

 ature, one finds that the above statement rests upon the descrip- 

 tions given about 1850 by Leuckart for the genus Ticnia and 

 closely related forms. This account was confirmed and supple- 

 mented by other authors about the same time, but in recent years 

 we only find the process referred to as something established 

 beyond all question as the universal method by which proglot- 

 tids originate. No recent work so far as I am aware attempts to 

 call this dogma in question, nor do writers longer think it worth 

 while to record the fact that they have confirmed so well estab- 

 lished a phenomenon. 



Despite this universal acceptance our current description 

 appears to be based upon published accounts which deal with a 

 limited number of forms, though the fact that these accounts 

 have not been contradicted leads one to believe that they describe 

 the process correctly in those species which have been most fre- 

 quently the subject of investigation. 



The cestode, Crossobothrium laciniatiuii, a species occurring as 

 an adult in the "sand shark," Carcharias litforalis, of our North 

 Atlantic coast, does not conform to the current account in itc 

 method of forming proglottids. In this cestode there first appear 

 from behind forward a considerable number of proglottids (Figs, 

 r, 2 and 10 of PI. IV.). These " posterior " segments, as I shall 

 call them, continue to form after the accepted fashion until about 

 35 of them have been produced. They are marked off by 

 straight transverse lines and not until a considerably later period 



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