a, 
1879.] 209 [Minot. 
Clepsine!. In other animals the entoderm forms lateral diverticula 
(e.g., Sagitta, tunicates, brachiopods and Amphioxus), which are 
likewise said to be concerned in the formation of the mesoderm, — but 
whether these diverticula do really form the mesodermic tissues 
properly so-called is doubtful. In both modes of development, as 
well as in other cases, we still find the mesoderm to consist at an 
early stage either exclusively or in part of mesamoeboids. I will 
refer to Bobretzky’s observations on gasteropods?, Biitschli on 
Paludina?, Kowalewski on Pyrosoma*, Reichenbach on the cray 
fish®, Stecker on Calyptrza®. It were easy to add to these references. 
It has long been known that the cells of the mesoderm in verte- 
brates are usually plainly amoeboid, and several authors have seen 
their amoeboid movements. 
From this brief discussion it is evident that the two points neces- 
sary to establish our thesis cannot be certainly proved with our pres- 
ent knowledge — while on the other hand the view advanced of the 
primary importance of the amoeboid cells of the mesoderm is quite 
plausible. If its correctness can be demonstrated it will be interest- 
ing to have discovered it, because we shall then have determined 
primary histological differences between the three germinal layers in 
their earliest stages, as follows: — 
Epithelial. 
A. Small cells, mainly protoplasmatic. . . . . Ectoderm. 
B. Large cells, with much dentoplasm, . . . . Hntoderm. 
Amoeboid. 3 
C. Cells free in the cavity between the two prim- 
itive layers, ecto- and entoderm. . . . . Mesoderm. 
In publishing these preliminary remarks I wish to add that I intend 
them only as forerunners of a larger work upon which I am engaged, 
and in which I hope to discuss these questions at greater length. 
1 Whitman. Embryology of Clepsine. Quart. Journ. Micr. Sec., Lond., XVIII, 
(1877), p. 82-86 of the reprint. 
2 Bobretsky. Studien ueber die embryonale Entwickelung der Gasteropoden. 
Arch. f. Mikr. Anat., x11, 95, figs. 48, 77, 79, etc. 
% Butschli. Zeitschr. wiss. Zool., XX1x, 219, and XXvVII, 519. 
4 Kowalewski. Arch. f. Mikr. Anat., x1, Taf. xxXxXIx. 
5 Reichenbach, Zeitschr. wiss. Zool., XX1IX, 123. 
6 Stecker. Morph. Jahrb., 11, 536. 
PROCEEDINGS B.S. N. H.— VOL. XX. 14. OCTOBER, 1879. 
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