Morse.] 342 [March 19, 
outer and inner folds of the arms, in those worms possessing these 
appendages, as in the Polyzoa, Phoronis, and the Brachiopods. I 
sought in vain the works of Claparéde, Quatrefages and others, for 
a figure of a longitudinal section through the mouth of some worm of 
this character. Mr. Alex. Agassiz kindly gave me a large specimen 
of the Amphitrite ventrilabrum, from the Bay of Naples, and I made 
a careful longitudinal section through the head (Fig. 16). The right 
arm was developed in a closely wound spiral of several turns, and 
greatly exceeded the length of the left one. I have shown the latter, 
however, as it presents a clearer view of the twist and character of 
the arm, as well as the crenulated membrane, or brachial fold which 
borders the base of the cirri. In this section, as well as in the 
accompanying one of Lingula pyramidata, the cirri are partially 
removed, as they form a confused tangle, and thus obscure the parts 
that are desired to be shown. 
The mouth is bordered by two membranous lips, which in the 
Brachiopods are highly sensitive and movable in all those thus far 
examined. The mouth in Amphitrite, as well as in other worms of 
that nature, is placed in the same relation with the head, and points 
downward, as in the Brachiopoda. The almost membranous shells 
have been removed, and the dorsal pallial membrane is turned back, 
to correspond in position with the dorsal cephalic collar in Amphi- 
trite, which is normally 
turned back, as in Sa- 
bella and Serpula. In 
other respects the sec- 
tions are correct draw- 
ings of their leading 
features, and are in no 
way modified to resem- 
_ ble each other. I have 
lettered the parts alike, and their almost absolute identity may be 
readily seen without further comments. The relations insisted upon 
as existing between the cephalic collar of the Annelids possessing 
it, and the pallial membranes of the Brachiopods, are well shown in 
these sections. Even the relative position of the base of the dorsal 
cephalic collar in the worm, corresponds to the same parts in Lingula 
and Discina, the dorsal one springing from the head in advance of 
the ventral one. See also Fig. 8, p. 14. 
Figures are here given of a young Discina, Fig. 17, and of a 
Fig. 17. 
Head of Discina. Head of Sabella. 
