THE TEMNOCEPHALO1DEA 45 



know that its true position is among the Platyhelmia. It occurs 

 in the Australian region, in New Zealand, in Celebes, Madagascar, 

 Chili, and Brazil. The other two genera are known only from 

 Australia. 



The most interesting anatomical feature, and one which differen- 

 tiates the class from the Trematoda, is presented by the external 

 covering of the body, for the epidermis retains to a great degree 

 its original character of a cellular layer, but the cells are not dis- 

 tinct ; they form a syncytium, in which the round nuclei are disposed 

 regularly (Fig. I. 5). This epidermis has, however, so far lost 

 its original character as to be deprived of cilia in most species, 

 and gives rise to a cuticle, varying in thickness, traversed by " pore 

 canals " for the passage of the necks of subepidermal gland cells, 

 which may contain rhabdites similar to those of Turbellaria. In 

 this latter respect, then, the class resembles the Rhabdocoelida, 

 and this resemblance is increased by the fact that in at least two 

 species, T. minor, Hasw., and T. dendyi, Hasw., vibratile cilia have 

 been recognised over the general body surface. The subdermal 

 rhabdite glands form rod tracts (Stabchenstrasse), as in many 

 Ehabdocoels, and are arranged in definite groups. 



The tentacular prolongations of the body are peculiar to the 

 group, though the Rhabdocoel Vorticeros presents two such pro- 

 cesses. The muscular system is specially developed and modified 

 at the posterior end to form a "sucker"; there are (a) fibres 

 which pass dorso-ventrally from the body wall to the centre of 

 the sucking disc ; (b) dorso- ventral fibres traversing the substance 

 of the sucker itself ; (c) circular fibres ; (d) radial fibres ; and (e) 

 certain longitudinal fibres from the ventral wall of the body into 

 the lateral part of the sucker peduncle. By the varying con- 

 traction and extension of the muscle fibres, this sucker is enabled 

 to attach itself firmly to any underlying surface. The possession 

 of the sucker naturally allies the forms with the Trematoda. 



The pharynx retains a somewhat primitive character in being a 

 Ph. bulbosus, whose chief function is " sucking." 



The excretory system of Adinodactylella is known only from 

 its flame cells ; but in the Temnocephalidae it presents certain 

 peculiarities, in that the number of component cells is very few, 

 and the nuclei of considerable size, recalling in both features the 

 Nematode excretory system ; for instance, each terminal contractile 

 sac is formed of a single cell. In addition to flame cells of a 

 normal structure, some of the branches of the system of capillaries 

 terminate in large cells, one to each such branch, riddled with a 

 number of very fine canalicules, giving rise to a structure recalling 

 very strongly the cells of the nephridium of Hirudo (Fig. I. 8). 

 The anterior position of the excretory pore, its contractile sac, and 

 the main course of the canal are features of resemblance with 



