Mr. L. F. Ward on Mesozoic Dicotyledons. 383 
stage runs nearly or quite equatoreally, namely, if a change of 
position of the first four segmentation-spheres round a right 
angle has occurred. By further divisions, all of which really 
run parallel to one another and appear to be radially directed 
towards the centre of the embryo only in consequence of the 
continued incurvation, the stage fig. le (section) is produced ; 
this already shows a distinct cavity, which, however, is still open 
at the inferior surface. Finally, this stage passes, in an easily 
intelligible manner, by further increase of cells and final closure, 
into the blastula, which, according to our view, originates in 
accordance with the blastula of the Volvocineze. All the cells 
of this blastula are still composed of the two elements, the 
ecto- and entodermal parts, which are now severed by an equa- 
toreal groove dividing each cell into an external and internal 
portion (fig. le). The cutting off of the entodermal portions of 
the delamination-blastula appears not always to proceed so 
uniformly as is here represented in accordance with the process 
demonstrated in the Geryonida by Fol and Metschnikoff. At 
least the representation that Kowalevsky gives of the delamina- 
tion in Encope seems to indicate that the division sometimes 
takes place successively, and thus the central cavity of the 
blastula is gradually filled with the entodermal cell-material. 
That here perfectly solid entodermal contents are first of all 
produced, in which an archenteric cavity only subsequently 
makes its appearance, may certainly be regarded as a secon- 
dary variation. The Siphonopora, however, present another 
variation of the delamination-blastula, as in them the develop- 
ment of a blastula-cavity is suppressed, and an archenteric 
cavity is only subsequently developed in the entodermal cell- 
mass. The reference of this modification to the mode in the 
Geryonida, which I regard as the original mode, appears to 
present no particular difficulties. 
XLIV.—On Mesozoic Dicotyledons. By Lester F. Warp*. 
In the following remarks on Mesozoic Dicotyledons, I con- 
fine the term Dicotyledons to that subclass of the vegetable 
kingdom which is embraced under the term Angiosperms in 
most modern text-books of botany. This is the usage of 
most vegetable paleontologists T, and the reasons of adopting 
it have been frequently statedf. 
The Dicotyledons occupy somewhat the same position in 
the history and development of plants that the Mammalia 
occupy with respect to animals. They constitute the domi- 
nant type, and in their rapid march have now so completely 
* From the ‘ American Journal of Science,’ April 1884, pp. 292-803. 
+ Goppert, Geinitz, and one or two others conform to the Jussizan 
system. 
t See the ‘ American Naturalist,’ yol. xii. (June 1878), pp. 359-878. 
