674 THE AMERICAN NATURALIST. [VoL. XXXIII. 
clearly that the embryo is formed by concrescence. At first the 
embryo increases in length largely by the formation of new somites, 
but after about one hundred myotomes appear, growth seems to be 
more in the increase in size of the somites. Especially noticeable are 
the large blood sinuses which develop around the embryo. No sec- 
tions are described in the paper. 
The Primitive Pulmonate Kidney. — Meisenheimer points out 
(Zeits. wiss. Zool., Vol. LXV, 1899) that the apparently distinct types 
of primitive kidney found in Stylommatophora and Basommatophora 
can be reduced toa simple tube, closed at its inner end by a differen- 
tiated ciliated cell. In the process of differentiation the tube of the 
Basommatophora retains constantly four cells, while in the Stylom- 
matophora the number is greatly increased. In the Basommatophora 
one cell becomes greatly enlarged, and in this the process of excre- 
tion is concentrated, while no such giant cell is developed in the 
other group, but excretion is performed by many cells. It is difficult 
to homologize this system with that found in other molluscs. Meisen- 
heimer points out the similarities of this system to the conditions 
occurring in the Plathelmenthes, and cites this as an additional proof 
of the origin of the molluscs from the flat worms. 
Life History of the Dicyemids.— As a result of studies of 
Californian dicyemids, Wheeler concludes (Zoo/. Anz., Bd. XXII, p. 
169, 1899) that the same Dicyema is first nematogen and later rhom- 
bogen, and that the so-called infusoriform embryo is, as van Beneden 
suggested, the male dicyemid. From the relations of the infusorigens 
and the life history of the animals Wheeler concludes that the male 
dicyemids arise from fertilized eggs, while the females are produced 
parthenogenetically. Wheeler points out that this interpretation 
throws little light upon the systematic position of these forms, since 
their reproduction is very different from the flat worms. He thinks, 
therefore, that they should not be an Anhang to the Plathelminthes, 
while he also thinks they are not worthy of being erected into a sub- 
kingdom Mesozoa. 
Origin of the Cartilages of the Head. — Lundborg has studied 
embryos of trout, frog, siredon, and acanthias, and comes to the 
conclusion (Morph. Jahrbuch, Bd. XXVII, p. 242, 1899) that the 
chondrocranium is of ectodermal origin. He calls attention to 
the fact that all of the cartilages of the head arise upon the ventral 
