EMBRYOLOGY AND ASEXUAL REPRODUCTION. Ech. 39 
The first trace of them is an ectodermic pit, at the base of which the 
epithelium grows rapidly to form a cellular papilla ; after which the 
median ventral radial canal sends out an evagination, which carries the 
cell growth at the base of the pit before it. The primary tentacle 
canals are from the first outgrowths of the radial canals. The rudiment 
of the central nervous system arises as a circular ectodermal ridge on the 
floor of the oral pit, sending out five prolongations in the direction of the 
radial canals. The mouth breaks through at the base of the oral pit. 
The foregut is not ectodermal, but endodermal. The enterocoeles sur- 
round the gut and form, a dorsal mesontery, but break through to one 
another at their ventral point of contact. On the fifth day the nervous 
system separates from the ectoderm proper, and the epineural canals are 
formed. The radial nerves and epineural canals grow backwards with 
the radial water canals. The stone canal now has a bulging of its 
walls, the future “ madreporic vesicle,” which from its mode of origin 
cannot bo looked upon with Bury as an anterior entoroccele. The 
tentacle which lies in the mid ventral line of the larva becomes the left 
ventral primary tentacle. At the end of the sixth day the first traces of 
the calcareous skeleton appear on the stone canal, the ring canal, and the 
foot canals. They are formed in the mesenchyme. On the ring canal are 
placed the five rudiments of the radial pieces of the calcareous ring. 
The mesentery is shifted to the left near the stone canal, and further 
back it is fixed to the left dorsal region of the body, then to the left 
ventral, and finally to the right ventral region. The mesentery thus 
takes the same course as in the adult, and forces a corresponding bending 
of the gut. On the seventh day longitudinal fibres are beginning to 
appear in the nervous system. The hyaline papillae appear on the ten- 
tacles as cuticular structures. The longitudinal muscles of the hydrocoele 
and the tentacle valves begin to form. 
Ludwig (5) describes the ontogeny of Holothurians under the following 
headings : — I. Season of Reproduction, pp. 249 & 250. ii. Preliminaries 
of Development, pp. 251-253. in. The Development of the Larvae, 
pp. 253-277. iv. Further Development of the Individual Organs, 
pp. 278-302. 
Perrier (4) describes the method of fixation of the young in some 
incubating species of Starfish. In Asterias spirabiUs , Bell, the young, 
the number of w r hich does not seem to exceed twenty, are collected in 
the centre of the lower surface of the disc, and entirely mask the buccal 
orifice (pi. i, figs. 1 & 2j). They are arranged obliquely, with a side of 
the disc towards the mother. It appears that during the whole period of 
gestation the mother takes no nutriment. The facts observed indifferent 
specimens indicate that the young are attached to the stomachal mem- 
brane of the mother, which undergoes a hernia to the exterior to support 
them. The young are fixed by a short peduncle, or “ umbilical cord,” 
through which they perhaps derive nutrition from the mother. This 
umbilical cord does not arise exactly from the centre of the inferior 
aspect. In position and aspect it is absolutely identical with the 
