672 THE AMERICAN NATURALIST. [VoL. XXXIII. 
delphinodonta, and W. proxima, from the coast of Maine, is given by 
Dr. G. A. Drew! The mantle of Yoldia is supplied with two pairs 
of sense organs and a fringe of marginal tentacles. There is also an 
unpaired extensible siphonal tentacle which is protruded upon the 
surface of the mud in which the animal is buried. Development 
shows that this is homologous with the marginal tentacles. The foot 
of all the forms studied serves as a burrowing organ, not as a struc- 
ture for creeping, as has often been supposed. The palps are active 
collectors of food, and the gills in Yoldia are very efficient pumping 
organs. The otocysts are provided with degenerating canals which 
lead toward the surface, and the genital ducts join the outer, not the 
inner, ends of the excretory organs. The eggs of N. de/phinodonta 
are carried in cases of mucus-like material, while those of the other 
two species are cast free in the water. The embryos of the first- 
named species have no locomotor bands, and a feeble apical cluster 
of cilia, and their development is less rapid. The species of Nucula 
agree with Yoldia, which has been most fully studied,’ in the forma- 
tion of an ectodermal “ test ” which is afterwards cast off. From this 
primitive covering the definitive ectoderm, the nervous system, and 
the stomodzum are formed. The openings of the proctodeum and 
stomodzeum are close together in the region of the primitive blasto- 
pore. At the time of metamorphosis the stomodzum, from its primi- 
tive opening to the position of the adult mouth, is cast off, together 
with a part of the apical plate. The test of these protobranchs is 
held to be the homologue of the velum of the molluscan larva, which 
has developed from ancestors resembling the embryos of Yoldia and 
Nucula in form and structure. Chiton, Teredo, Cardium, and Poly- 
dordius are known to cast away the velum of the larval stage. The 
test of the protobranchs is strikingly similar to that found by Pruvot 
on the embryo of Dondersia one of the primitive group of Soleno- 
gastres. CAR 
Innervation of the Pharynx. — The innervation of the laryngeal 
muscles is an important point in settling their homologies with the 
muscles of the branchiate vertebrates. The usual statement is that 
the recurrens nerve supplies all the muscles except the M. cricothy- 
1 Drew, G. A. Some Observations on the Habits, Anatomy, and Embryology 
of Members of the Protobranchia, Anat. Anz., Bd. xv, Nr. 24 (1899), pp. 493-519. 
With 21 figures. 
2 Drew, G. A. Yoldia limatula, Mem. Biol. Lab. J. H. Univ., vol. iv, No. 3 
(1899), 37 PpP» 5 pls. 
