CyiilicoYCM^ from a rare /^oljt/un. 423 



As rof^nrd'^ the (liinciisions of tlio scolcx, tlio pros^nt form 

 seems to approncli most closely to J/, eleijutift, wliicli has 

 been fairly fully described by both Zschokke * (18^9) and 

 de Beaucliam[) {lOOf)). Tho length of the scolex in this 

 form is piven by Zschokke as O'i inm.-08 mm., the width 

 of the scolox as 0*3 mm.-0'4 mm., and the width of the neck 

 as Ol nim.-0-25 mm. Tho other measurements given by 

 both authors agree fairly well with those given above for 

 the cysticercus. 



There has been some confusion between M. perfectum 

 (van Benedeii) and M. eJegans, but on comparing the original 

 descriptions it seems liiglily probable, as Monticelli (1890, 

 p. 4.^-4, footnote) and dc Beauchamp (1905) contend, that the 

 two forms arc distinct. ^[. elegans, according to de Beau- 

 champ, is 17 or 18 cm. in length, while M. perfeclum reaches 

 30 to 40 cm. (van Beneden, 1853, 1861) or 12 to 15 inches 

 (Diesing, 1863). The scolex is also very much larger in 

 M. perfeclum^ measuring, according to van Beneden, 1-2 mnj. 

 in width, while Diesing gives it as ^-1'". M. perfectum 

 would apjiear t leretore to be a considerably larger form 

 altogether than M. elegans. 



LlFE-IIlSTORY. 



It would have been extremely interesting if the cysticercus 

 under discussion could have been shown to belong to Mono- 

 rygma perfeclum, since, as Dr. S. F. Uarmer intorms me, the 

 host of this S|)ecios, the Greenland shark {Lcemargus borealis) 

 has the habit of biting out pieces of the flesh of living 

 Cetacea, and this would have afforded a satisfying account of 

 the life-history of the [)arasite. If M. elegans and M. per- 

 fectum were sliown to l)e identical, greater plausibility might 

 be lent to this hypothesis. For the present, however, it 

 seems impossible to assign the cysticercus definitely to any 

 of the species. It may very possibly be that of M. elegans, 

 which is parasitic in Scyllium spp., and to which species, as 

 has been seen, it approaches closely in the size and structure 

 of the scolex. We have also to remember the somewhat 

 lemarkable fact that the cysticerci can remain alive for at 

 least eleven ilays after the death of the host, and even alter 

 its removal trom the water. Hence they may very well be 

 swallowed by any species of dogfish that devours pieces of 

 dead dolphins containing the cysts. 



* Zschokke describes it under the name of -V. perfectum. Dies. 



28* 



