AND HABITS OF THE AMMOCHARIDA. 251 
proceeds to force them into the sand. In this operation it is 
assisted by the “ Lippen-organ,” the ventral end of which, acting 
very much like the foot of a mollusk, strikes over the edge of 
the membranous tube, and so, with its underside, digs a burrow 
in the sand, enabling the animal gradually to screw itself down- 
wards. The “thoracic” setz also appear to take part in this 
work. This operation is much slower and more laborious than 
the upward burrowing, and the animal not unfrequently cuts off, 
and leaves on the surface, a portion of the tube. The tube 
is thus re-embedded in its natural position; and it is very un- 
usual indeed to find a tube in which a change in the direction 
of building has taken place, though I am bound to admit this 
occasionally occurs. 
With reference to the method of reproduction, Claparéde (6), 
von Drasche (12. p. 20), and Gilson (30. p. 99) have respec- 
tively described the formation of the sexual elements as taking 
place on the walls of the ventral blood-vessel, in the tissues 
which clothe the longitudinal muscles, mesenteries, and blood- 
vessels, and on the inner face of the musculo-glandular tissue, 
of which the last-named author considers the body-wall of 
Owenia to be composed. All agree that the elements are shed 
into the body-cavity, that they float about in the ccelomic fluid, 
and are frequently found, apparently straying, in the “‘ thoracic” 
and buccal segments. The means of their escape from the 
body-cavity is unknown, though Gilson (27. p. 370) confidently 
suggests that the “ epithelial canal” in the second “‘ abdominal ” 
segment is the natural outlet. Starting from this standpoint, 
I have directed my attention, firstly, to observing the movements 
of the ova when they appear in the cephalic segment; and, 
secondly, to ascertain in the living animal the mode of emission 
of the sexual elements, and the early life-history. 
By the first line of research I failed to secure the information 
I desired, namely, as to the fate of the ova in the cephalic seg- 
ment, though it resulted in the discovery of the interesting, and 
probably unique structure for a Polychete, the opening of the 
cephalic lobe (c.p., Pl. 24. fig. 8). Although this structure is 
exceptional in the Polycheta, a similar prostomial pore is met 
with in some Oligocheta (Enchytreide), a fact to which Mr. E. 
S. Goodrich has kindly called my attention. Upon this point 
Beddard makes the useful contribution that ‘“ the dorsal pores 
are missing without exception in those Oligocheta which live in 
