1901.] NATURAL SCIENCES OF PHILADELPHIA. 719 



that the large hlood lacuna occupies the entire space within the 

 muscular wall of the caudicle of Zijgeupolia, and that the mesen- 

 chym — blood-forming — cells are very abundant, suggests that one 

 function of the caudicle may be the formation of new blood cells. 

 This, however, also takes place throughout the blood vessels of the 

 body. The large blood lacuna of the caudicle is probably a 

 means of aerating the blood, making respiration another possible 

 function of this jiroblematical structure. 



Literature of the Caudicle. — The caudicle has been known in 

 literature under various other names, and considerable confusion 

 has arisen from the multiplication of terms, and from the fact that 

 the caudicle, which is an adult structure, has been confounded 

 ^vith the regenerating " papilla" so frequently found at the poste- 

 rior end of Nemerteans that have been broken. 



For this reason an account of the history and synonymy of the 

 caudicle and the differences between the true caudicle and the 

 regenerating posterior end will be given, at perhaps greater length 

 than the importance of this small structure demands. 



The following papers will be separated under two headings I, 

 those describing the true caudicle; II, those in which other struc- 

 tures have been mistaken for the true caudicle.^' 



I. Ehrenberg and Hemprich (1831) describe the new genus 

 Micrura with " anus sub caudo," and Micrura fasciolata nov. 

 sp. , " . . . . anus terminalis sub processu caudali parvo, albo." 



Busch (1851) (cited by J. Miiller, 1854) mentions and figures, 

 Taf. II, Fig. 8, a Nemertean with a caudicle (" Schwanzan- 

 hang"). The worm is described under the name of Alardus 

 caudatus. 



Diesing (1851) refers to Micrnira Hemp, et Ehr. = Nemertes 

 Oersted, as with a " processu terminali postico filiformi brevis- 

 simo. " He describes the new species Meckelia Knerii Diesing, 

 ' ' corpus depressuni retrorsum parum augustatum processu brevis- 

 simo filiformi." 



Dalyell (1853), Vol. II, (cited by Krohn, 1858), describes 

 under the name Gordius four Nemerteans that would now be 



'^ lu this review of the history of the caudicle some of the earliest and 

 some of the most important papers in Nemertean literature are referred to, 

 but no attempt has been made to give a complete list of all the observations 

 on the subject. 



