REPTILIAN TAPEWORMS. 11 



parasite of Varanus niloticus within the species Ichthyotcenia 

 tidswelli, excepting, indeed, the presence in the latter of" a layer of 

 longitudinal muscular fibres in proglottids with fully developed 

 testes. These muscles I can only find anteriorly in my species. 

 It appears to me, however, to be imprudent to give a name to the 

 Ichthyotcenia which I haA'e just described until a good deal more is 

 known about its anatomy than is contained in the present paper. 



In addition to the small species which has just been described, 

 Varanus niloticus is infested by a larger Ichthyotcenia which 

 I term I. nilotica, regarding it as an undescribed species. 



I am uncertain about the length, inasmuch as I had to deal 

 with fragments only of various sizes. The largest fragment with 

 a scolex attached measured about 20 mm. But as the posterior 

 region of this piece had not nearly acquired the dimensions of 

 obviously mature fragments, at least 10 mm. can be, I think, safely 

 added on to the length. The species is fairly slender, but not in 

 the least thread-like, and the stoutest proglottids do not reach 

 much more than "5 mm. in diameter. The most salient external 

 feature of this species differentiates it at once from Ichthyotcenia 

 varia and /. gracilis ; there is no external appearance of seg- 

 mentation without a careful examination with a lens. Only the 

 slightest constriction marks the boiindary line of adjacent pro- 

 glottids. In this feature the present species agrees with /. biroi 

 and /. ticlstoelli. The i^ipe segments get to be longer than broad, 

 but they are apparently never very long. 



The scolex has the usual Ichthyotaeniid characteis. I only 

 found two scolices, and in both the conical rostellum was long 

 and is possibly therefore not retractile. The four suckers are 

 clustered round its base and look forwards. I observed the usual 

 dense investment of spinelets which led v. Linstow to bestow^ the 

 name of Acanthotcenia upon the genus. One of the two scolices 

 was cut into a series of transverse sections for the purposes of 

 further investigation. At the apex of the rostellum there was a 

 distinct sucker-like depression carried on a narrow prolongation 

 of the rostellum, which, however, showed no such great spe- 

 cialization in its tissues as the four suckers proper, though it is, 

 I am sure, a permanent structure and not a mere temporary 

 involution of the rostellar region. Such a structure has been 

 discerned in other species of reptilian Ichthyotcenia, and has been 

 regai'ded as the homologue of the rostellum of other tapeworms. 

 In the smaller Ichthyotcp.nia from Varconns niloticus that has just 

 been described the apical structure was obviously of the nature 

 of a retractile rostellum. 



The four suckers are borne upon prolongations of the scolex in 

 which lie water-vascular tubes, which latter were not quite so 

 conspicuous as in the last mentioned species of Ichthyotcenia. 

 It is these outgrowths of the scolex that are the motile parts of 

 the scolex when the suckers are protruded or withdrawn. To a 

 naked-eye examination the svickers appear to be sessile upon 



