'I'HK DEVELOPJrKNT OF THE TEMNOCEPHAl.E.E. 
437 
mass of primordial cells surrounded by indifferent cells. In 
T. novae-zealandite before the young animal leaves the egg 
the first stages of spermatogenesis have occurred. At this 
stage the atrium does not yet open on the exterior. The 
definite development of the female part of the apparatus does 
not begin till after hatching, so that AVacke’s statement 
that Temnocephala is protandrous appears to have some 
evidence in its favour, though a study of the post-larval 
development will be necessary in order to decide whether 
the condition is one of actual functional protandry, and not 
mei’ely one of more active development of the male apparatus 
in the early stages. 
The unique features of the early development of Temno- 
cephala are associated with the formation of the remarkable 
internal cavity (endocoele) around which the foundations of 
various systems of organs are laid down. As nothing parallel 
to this cavity has, so far as my knowledge extends, been met 
with in other groups,^ it is natural to inquire if its pi’esence 
can be associated with any special conditions under which 
the development takes place — if its occurrence can be sup- 
posed to be of the nature of an adaptation. 
The Australian fresh-water Crayfishes, on which live all 
the known Australian members of the Temnocephalefe, shelter 
or support a great variety of small Invertebrata. A consider- 
able proportion of these live in the branchial cavities, but many 
adhere to various parts of the outer surface. Among sucli 
dependents of the Ci’ayfishes are Protozoans, Nematodes, 
Rhabdococles, Rotifers, Stratiodrilus, Phreodrilus, a parasitic 
Ilydrachnid, and others. In a country subject at times, 
as Australia is in many parts, to long-continued di’oughts, 
* It might 1)6 possible to trace some coiniection between the embryonal 
pharynx of the Tricladida (Halle/. [6], Metscbnikoff 112], lijima [10] ) 
and the endocoele of Temnocephala. Both cavities arise as spaces in 
rounded groups of cells in the blastoderm ; but the former opens on the 
surface and swallows yolk cells, with which the intestine becomes dis- 
tended. Moreover it is jmrely provisional, and disappears entirely, a 
new pharynx becoming developed in its place. 
