Haswett—A Monograph of the Temnocephalee. 99 
the other monogenetic forms may lead to a similar discovery with regard to them, 
and thus the distinction in this respect between the Trematodes and the 7urdellaria, 
usually supposed to be absolute, may be broken down. But, so far as our present 
information goes, 7emnocephala occupies in this respect, as in certain others, a quite 
unique position if it be regarded as a Trematode. When I published the previous 
paper already referred to, I had entirely overlooked this remarkable fact, owing to 
my having at my command only spirit-specimens of the species ( 7. mezzo) in which 
the structures in question are best developed. In this species the cilia are most 
numerous and active immediately behind the tentacles ; but in many individuals are 
present in more scattered fashion over the rest of the surface, with the exception of 
the tentacles and the sucker, on which they never occur. In 7. Dendy7 they are less 
numerous than in 7. mzxov, and I have only hitherto succeeded in detecting their 
presence in that species towards the lateral border of the body on the dorsal aspect 
just behind the bases of the tentacles, from which point they extend backwards a 
considerable distance beyond the excretory sac, though never as far as the middle of 
the body. Where they occur they stand in marked contrast to the non-motile cilia 
of the tactile cones about to be described—being curved, highly flexible and whip- 
like; they are intermediate in character between ordinary cilia and the flagella 
(Geisseln) that occasionally occur here and there on the surface of a Rhabdoceele 
Turbellarian. They do not oceur in 7: fasczata nor in 7. Nove-zealandi@ at any 
stage. Both Semper and Weber state that they are absent in 7. Sempert. 
A second set of integumentary structures, previously overlooked by me and not 
noticed by Weber or Braun, seem to be universally present. These are minute 
elevations in the form of truncated cones (005mm. in height in 7. fasczata) which 
occur abundantly on the anterior part of the body and on the tentacles (Pl. x. fig. 1, 
¢.c.); each has at its summit a little fasciculus of non-motile cilia. In all probability 
these are integumentary sense-organs, and, though I have not completely traced 
a direct connection with nerve-fibres, it would seem likely that they form the 
end-organs of the extremely complex subcutaneous nerve-plexus, since numbers of 
nerve-fibres are given off from the transverse branches of the dorsal nerves and run 
straight through the layer of longitudinal muscular fibres towards the epidermis. 
Sunilar structures, differing somewhat in shape, have been described by Wright and 
Macallum* as occurring in Sphyranura Oslerd, and have been named by them the 
‘tactile cones.” 
The integument in 7enocephala and Craspedella is wnique among Trematodes 
in consisting of three well-defined layers, which may be termed cuticle, epidermis, 
and basement membrane. The caézc/e (Pl. x. figs. 1, 2, 7 and 8, cz.) is readily discernible 
2 * «Sphyranura Osleri: a Contribution to American Helminthology.” ‘Journ. of Morphology,’ Vol. I. p. 9, pl. 1. 
g. 2. 
