No. 395.] REVIEWS OF RECENT LITERATURE. 893 
Envelopes of the Spinal Cord. — Sterzi has studied this subject 
from a comparative standpoint (Anat. Anz., Bd. XVI, p. 230) and 
points out that in the fishes there is but a single envelope proper, 
the meninx primitiva. In the Amphibia two meninges are developed, 
a meninx secundaria and a dura mater, separated by a series of 
lymph spaces. In the mammals these are represented by the three 
well-known membranes. In development the various meninges are 
developed from a single meninx primitiva by the formation of lymph 
spaces. Above the dura is an epidural space, whose lateral walls are 
formed by the so-called “ Kalkorgan,’’a membrane with numerous cavi- 
ties, containing crystals of calcic carbonate, but which is not to be 
considered as one of the true envelopes of the cord. The endo- 
rhachis is a strong fibrous membrane which serves as the periosteum 
of the spinal canal. 
Origin of Mammals. — In the discussion on the origin of the 
mammals’ recently held at the fourth international congress of 
zoology, Professor Seeley stated as his opinion that the anomo- 
donts were not ancestors of the mammals, but that both groups had 
a common ancestor to be sought for in rocks earlier than the 
Permian. ‘The forms thus far discovered, however, show so close 
a connection between reptiles and mammals that it is not reason- 
able to believe that future discoveries will seriously alter this 
assumed connection. Professor Osborn believed that much of the 
resemblance between reptiles and mammals was due to parallelism 
and pointed out that the mammal egg was more amphibian than 
reptilian in character. If the ancestor of the mammal was a reptile 
it was one that retained certain amphibian characters. Professor 
Marsh expressed the opinion that none of the fossil reptiles thus 
far known could be said to be a satisfactory ancestral representa- 
tive of the mammals and suggested the origin of this group from 
primitive amphibians. Professor Haeckel argued for the mono- 
phyletic origin of placental mammals from one marsupial ancestor. 
Mr. Sedgwick thought the question of the origin of mammals was 
possibly insoluble from the facts that embryological evidence is not 
sufficiently conclusive and that the paleontological remains are too 
fragmentary. Professor Hubrecht defended the view that mammals 
may have had a polyphyletic origin and raised the question whether 
mammals other than monotremes had descended from oviparous 
ancestors. 6G HP 
1 The Origin of Mammals, Proc. Fourth Internat. Congress Zoöl., pp. 68-75. 1899. 
