LIFE-HISTORIES OF TREMATODES 



71 



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 1 never found 

 intermediate hermaphrodite conditions, 

 this Distomum may be almost certainly 

 regarded as of distinct sexes. Didymo- 

 zoon thynni (Monostomum bipartiturri), 

 from cysts on the gills of the Tunny 

 (Tkyrmus), is another case. Two slender 

 worms flattened posteriorly, come to- 

 gether, and the body of one becomes 

 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 Nematohothrium (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. 



Fig. 35. Distomum okenii KoU. 

 Showing male and female as 

 they occur together in the 

 branch ial cavity of Brama raii 

 (Ray's bream). (FromBronn, 

 after Kolliker. ) Nat. size. 



Table of Digenetic Trematodes and their Life-Histories. 



Species. 



Final host. 



. 



Iplodiscus (Am- [ J> ./ 



phistamum)sub- J * Bu f> 



clavatus Gbze (_ 

 Distomum advena C 



Duj. (D. mi- -J Sorex araneus 



grans Duj.) 

 D. appendicular 



f) m Rud. 



Til 



Host into which the 

 larva enters, and in 

 which Cercariae are 

 eventually formed. 



Smaller species 

 Planorbis 

 Cyclas 



eventually iormeci. 

 f Smaller species of f 

 -J Planorbis and -J 

 \ Cyclas \ 



Host into which the Cercariae 

 migrate and encyst ; eaten by 

 final host. 



Insect - larvae, Sana, Bufo, 

 but frequently omitted 



Not known 



Limax 



\ Clupea 



alosa 



Not known 



ascidia v. Ben. 



Species of Bats 



D. atriventrc f Frogs and Toads 

 WeinL \ of N. America 



D. brachysomum j The Dunlin / 



Crepl. \ (Tringa alpina)\ 



D. caudatum v. f Hedgehog (Erina- f 

 Linst. \ ecus europaeus) \ 



J Lucullus acuspes, Centropagcs 

 \ hamatus (Copepoda) 

 ( Limnaeastagnalis ( Ephemera, Per la, Chironomus 

 \ Planorbis comeus \ plumosus 

 Physa heterostro-f^ otkno ^ n 

 pha y 



Not known 



Helix hortensis 



Anthura gracilis 



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



2 Braun, loc. cit. p. 573. 



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

 subject is referred to fully. 



