DEPARTMENT OF EMBRYOLOGY. 101 



has been continued here in Baltimore. The intrauterine period of the 

 opossum is only of 13 days' duration and the intestinal nutrition must 

 therefore commence while the animal is still quite inunature. There 

 is thus offered an unusual opportunity to observe the factors in this 

 process under the most primitive conditions, before there are any in- 

 testinal glands or muscle coats. The striking feature of the intestine 

 of opossum embryos at the time of their transferral to the pouch is the 

 presence of numerous large sinusoidal blood-vessels which closely hug 

 the mucosa. The latter makes up nearly the whole thickness of the 

 intestinal wall and consists of tall villi covered by columnar cells which 

 contain characteristic masses of granules in their distal ends. 



Dr. Lineback finds that in human embryos the longitudinal muscle 

 can be recognized at the caudal end of the colon in embryos 40 mm. 

 long and then rapidly extends towards the coecal end. It appears first 

 along the mesenteric line and soon spreads to incase the whole tube, 

 forming a complete envelope before the tsenise appear. The mesen- 

 teric portion thickens and forms the first taenia and the others are defi- 

 nitely formed by the time the fetus is 105 mm. long. Dr. Lineback 

 regards the sacculations of the wall of the colon as the result of the com- 

 bined action of the longitudinal and circular muscles. 



The work of Dr. W. H. Lewis on the development of the skull in a 

 21 mm. human embryo, referred to in Year Book No. 12, was pubUshed 

 during the past year. In the embryology of the skull there is great 

 need for a more complete and detailed series of the various stages, 

 showing the gradual development from the primitive membranous 

 form to that of the adult. Dr. Lewis's excellent description of the 

 skull of this embryo fills in one of the several gaps still existing in the 

 sequence of published stages. 



It has been anticipated that the primordial or cartilaginous skull 

 would bear many indications of phylogenetic relationships, but appar- 

 ently this is realized in only a few general features. Dr. Lewis finds 

 that the cartilaginous skull in the embryo is as characteristically human 

 as is the adult skull. It resembles the cartilaginous skull of other mam- 

 mals not more closely than does the adult skull of man resemble the 

 adult skull of such mammals. It is becoming more and more clear, 

 as our knowledge of its anatomy increases, that the human embryo 

 and its various organs are at all stages as characteristically human as 

 are the adult body and its organs. This is what would be expected if 

 it be true that evolution comes about through changes in the germ 

 plasm, for in that event the changes would appear in the egg and in all 

 the subsequent stages of ontogeny, and would modify the entire devel- 

 opment as well as the adult. There are, however, occasional anomalies, 

 giving fleeting indications of phylogenetic relationships that are diffi- 

 cult of interpretation. Such an anomaly is present in this case in the 

 form of an occipital vertebra. The occipital hemiarches are distinct 



