DEVELOPMENT OF CUCUMARIA ECHINATA 291 
Those which appear in the integument increase and develop 
rapidly and soon cover the body on its posterior half. Their 
shape 1s not quite regular, but is commonly a delicate lattice 
plate formed of successive dichotomous branchings of the 
original primary cross. They lie parallel to the surface em- 
bedded in the dermal connective tissue formed below the ecto- 
derm. 
According to Kowalewsky (1%, p. 6), in C. kirchs- 
bergii the calcareous body first appears in the wall of the 
stone-canal. Ludwig (22, p. 610) found in C. planci that 
deposits appear on the sixth day at three different places, 
i.e. the stone-canal, ring canal, and pedicel canal. I failed to 
notice the last-mentioned part in C. echinata, in which 
the deposits in the integument are most marked among the 
three kinds. Mortensen’s neure’ (Se, Pl i, fig. 8;.c) of 
the larva of Psolus phantapus represents a similar feature, 
where delicate lattice plates in the integument and the rudiment 
of the calcareous ring are shown. 
14. PENTACTULA. 
In this stage the ciliary bands have disappeared, the 
tentacular crown has assumed its terminal position from the 
diminution of the pre-oral hood, and at the centre of the 
tentacular crown the mouth is opened while the anus has 
appeared posterodorsally. This stage is reached as early as on 
the seventh day, as found among the Mitsukuri material. 
The larva now begins to creep on the bottom and to feed 
itself. 
The internal changes taking place at this stage may be described 
as the further completion of all the systems and organs which 
were roughly established in the preceding stage. A very con- 
spicuous feature of this stage as found in sections is the large 
space which the body-cavity occupies and the thinning out of 
every epithelium lining the water-vascular system and body- 
cavity. 
