II LIFE-HISTORIES OF TREMATODES 7 I 



the female organs. Until we certainly know that the swollen 



egg-bearing form (?) does not arise from a previously male 



form ( < ), the case is open to suspicion. 



Since, however, Kolliker l never found 



intermediate hermaphrodite conditions, 



this Distomum may be almost certainly 



regarded as of distinct sexes. Didymo- 



zoon thynni (Mbnostomum bipartitum), 



from cysts on the gills of the Tunny 



(Thynnus), is another case. Two slender 



worms flattened posteriorly, come to- 



gether, and the body of one becomes (Ray's bream). (FromBronn, 

 -,.'... ,_, mi after Kolliker.) Nat size. 



folded to receive that of the other. They 



fuse completely except for a small lateral opening through which 

 the anterior parts of both worms may freely protrude. The 

 enclosing individual contains a coiled uterus filled with eggs, 

 and is the female, whereas the smaller individual never possesses 

 eggs, and is probably the male. 2 Nematolothrium (Fig. 22, A), 

 which occurs also in the Tunny, in the form of two immensely 

 long individuals intricately wound about each other in a cyst, is, 

 however, not bisexual. 



Table of Digenetic Trematodes and their Life-Histories. 8 



Host lnto which the 



Species. Final host. riae are "** Md enc * st : ~ ton ** 



eventually formed. 



** 



Distomum advena f 



Duj. (D. mi- - Sorex araneus . Not known Limax 



D. atriventref Frogs and Toads Physa heterostro- f -^ . v _ rt 

 Weinl. I of N.America pha -^ Not known 



1 See Braun. Bronn's Klassen u. Ordnungen d. Thierreichs, vol. iv. p. 572. 



2 Braun, loc. eit. p. 573. 



3 Taken largely from Braun, Ibid. pp. 864-866, where the literature of the 

 subject is referred to fully. 



