THE CESTOIDEA 125 



The systematic position of this isolated genus presents considerable 

 difficulty ; it is evident that it is Tetrabothridiate both from the structure 

 of its suckers and from the absence of a distinct birth-pore. The fact that 

 the margins of the bothridia project freely and are slightly mobile points 

 to its affinity with the Tetraphyllidea rather than with the Taeniidae or 

 Tetrarhyncha, as also do the genital organs. Its long " head stalk " is a 

 point of resemblance to the latter group. This region is not one of 

 budding as is a " neck " in the rest of the Merozoa, for there is a sharp 

 demarcation between the region of budding and the armed region both 

 in Echinobothrium and the region which contains the proboscis sacs in 

 Tetrarhynchm. The fact that in both families there is a tendency for 

 the bothridia to fuse in couples must not be held to have great weight, 

 since in the Tetraphyllidea we find the same tendency in various genera. 

 The ventral genital pore too is not unknown amongst the Tetrarhyncha 

 nor the Tetracotylea, but at first recalls the Bothriocephalid arrangement. 



Probably Echinobothrium came off from the Tetrabothridiate stem 

 at a very early period, and has remained thus isolated. 



The genus Tetracampos, Wedl., may possibly be allied to Echinobothrium. 

 The scolex possesses four round, flat, feebly expressed phyllidia ; the 

 rostellum carries four groups of hooklets, but nothing is said as to its 

 retractility. The genital pores are on the ventral surface. The hexacanth 

 embryo is ciliated. T. ciliotheca, Wedl., in Heterobranchus anguillaris of 

 the Nile (Stzber. Akad. Wien. Math. Nat. Cl. I. xliv. 1861, p. 473). 



ORDER 3. Tetrarhyncha, v. Ben. ( = Phyllorhyncha, v. Ben. ; 

 = Trypanorhyncha, Dies.). 



The four phyllidia (bothridia) may be united in pairs, as in the 

 Diphyllidea. Each phyllidium is accompanied by a long spiniferous 

 proboscis (or " trypaiiorhynchus," Dies.) capable of retraction into a sac 

 occupying the " head stalk." The adults occur in Selachians. The 

 metacestode is encysted in various parts of Teleosteans. FAMILY 

 TETRARHYNCHIDAE ( = Dibothriorhyncha + Tetrabothriorhyncha, Dies., etc.), 

 with characters of the order. Syndesmobothrium., Dies. ; Tetrarhynchus, 

 Hud. ( = Rhynchobothrium, v. Ben., Lkt., etc.). The genus contains a large 

 number of species. T. ruficollis, Eysenh., in Mustelus, Acanthias, etc. ; its 

 metacestode is Coenomorphus joyeuxii, Lonnb., which occurs in crabs (Vaul- 

 legeard, 1895). Rhynchobothrium, Rud. (incl. var. spp. of Tetrarhynchus, 

 auct.) ; Otobothrium, Lint. ; 0. crenaticolle, Lint., from Zygaena malleus. 



Remarks on the Tetrarhyncha. The numerous species occurring 

 in sharks have been, by various authors, referred to a variety of 

 genera distributed over two families founded on the character of the 

 bothridia, whether they are two or four, independent or united. 

 Pintner in a recent work (34) would refer all species to one genus 

 Tetrarhynchus, for, as he points out, there is every gradation between 

 the various conditions of the phyllidia. 



The scolex in this group is extremely elongated, and, as in the 

 Diphyllidea, is provided with a very long " head stalk," which is 



