EMBRYOLOGY — GEOGRABHICAL DISTRIBUTION. 
139 
The development of the freshwater Pulmonata^ especially Limncea^ is 
also discussed by C. Rabl in Jen. Z. Nat. ix. pp. 195-240. 
O. Butschli makes some observations concerning the embryonal deve- 
lopment of Limncea auricularia (L.) and Succinea pfeifferi (Rossm.), 
from two to eight small vesicles being the first appearance of the nucleus 
of the future first segment of the yelk. Z. wiss. Zool. xxv. pp. 206 & 207. 
W. Flemming gives a very accurate and interesting account of the 
development of Anodonta (^piscinalis and anatina) and Unio {tumidus and 
pictorum) from the first formation of cells within the egg to the larval 
stage which is attached to fishes ; the further metamorphosis to the 
perfect bivalve has never yet been observed. The following are some 
of the more striking points of the author’s observations: — Formation of 
cells within the yelk by division very soon becomes unequal, in the 
segment called the under one by the author, the cells of each division 
being- of the same size, whereas in the opposed or upper segment 
each division is only the separation of a small new cell from a 
larger permanent one. In the following stage, the embryo exhibits a 
large internal hole, not formed by invagination or corresponding with 
the pallial cavity or intestine of the mature animal ; the pallial cavity 
is formed during the larval stage by invagination from below, not by 
cleavage, as supposed; the intestine was not apparent in the stages 
observed. The author finds it very difficult to apply to these facts the 
usual terms of germinal layers, endoderm and gastrula, and therefore 
brings forward a theory that one part of the yelk overgrows and 
embraces the other, which however his actual observations do not cor- 
roborate. Former publications on the development of these and other 
bivalves, are carefully compared and analyzed, and some remarks are 
added on the permanency or new formation of the cellular nucleus 
during the division of the yelk, and on epigenesis and evolution in 
general. SB. Ak. Wien, Ixxi. pt. 3, 132 pp., 4 pis. 
Teratology. 
Monstrosities of dausilia biplicata (Mont.) and rossmcessleri (Stentz) 
with a double peristome described by Westerlund, Nachr. mal. Ges. 1875, 
pp. 84 & 85 [already described and fully explained by Hartmann, Gas- 
teropoden d. Schweiz, 1844, p. 173]. 
Five sinistral specimens of Helix adspersa found in the same year near 
Epsom by J. E. Daniel, Q. J. Conch, i. pp. 50 & 51. 
A sinistral specimen of H. hortensis found at Bristol by F. M. Hele, 
tom. cit. p. 92. 
GEOGRAPHICAL DISTRIBUTION. 
a. Land and Frebh-watbr Mollusoa. 
1. Northern and Central Europe. 
The British land- and freshwater-shells are discussed in a popular 
treatise by J. E. Harting, parts of which have been published before in 
“ The Field” newspaper in 1873 & 1874 ; the author gives a general 
