184 
MOLLUSCOIDA. 
Hippocrepia. 
E. Metschnikopf has observed that in Alcyonella the eggs 
formed originally within the parent animal find their way into 
a sort of bud at the side of its body, and are there developed into 
the well-known larva. He describes accurately the first deve- 
lopment of it, with particular regard to the different germinal 
layers (Keimblatter) and the origin of the various tissues. Bull. 
Petersb. xv. (1871), p. 507. 
H. Nitsche confirms this observation, explaining how the 
larvie can leave the living parent body, although it possesses 
no genital orifice, since the bud eventually opens in the same 
manner as the sheath of the tentacles. The parent polypid un- 
dergoes a retrogressive metamorphosis, and ends by becoming a 
brown body,^^ as in Flustra {cf. Zool. Bee. viii. pp. 177 & 178). 
Z. wiss. Zool. xxii. pp. 467-471. 
Rhabdopleura (Allman, IS69) =Halilophus (M. Sars, Forh. 
Selsk. Chr. 1868, p. 112). Polyzoarium or zooecium forming 
a thin cylindrical chitinous hyaline tube, containing a chitinous 
rigid cord; polypids without endocyst, attached only by a 
contractile fleshy cord to the polyzoarium, without distinct 
muscles for retracting or protruding. Tentacles placed on two 
separate branches, between the bases of which is a shield-shaped 
fleshy prominence, like the foot of a snail, and behind it the 
mouth. Intestine well developed ; anal orifice near the base of 
the branches, upwards. R. mirabilis (M. Sars), Lofoden Islands, 
Norway, at a depth of 100-300 fathoms, with Rhizocrinus. 
Movement very slow. M. Sars considers it a very low (old) 
form of Polyzoa, retaining several affinities to the Hydroid 
Coelenterata, Sars, Eemarkable Forms, &c. pp. 1-18, pi. 1, and 
pi. 2. figs. 1-24. 
