358 MONTGOMERY. [Vou. XII. 
or (3) by invaginated diverticula of the entoderm (in Sagitta 
and Phoronis). It is a derivative of the gastrocoel when the 
coelomic sacks are evaginations of the entoderm (as in the 
Echinodermata, Balanoglossus, Brachiopoda, Ascideae, and 
Amphioxus). In the Ctenophora it is both gastrocoelic and 
archicoelic in origin. This cavity is called a pseudocoel when 
it is not lined by a continuous epithelium of cells, and a coe- 
lom when it has such a lining. The pseudocoel of a turbella- 
rian and the coelom of an annelid are both derivatives of the 
archicoel ; but the coelom of Amphioxus is gastrocoelic in origin. 
In the same animal, coelom and pseudocoel, when both cavities 
occur together, may communicate. From these facts we may 
conclude, that there is also no valid morphological distinction 
between a pseudocoel and a coelom, when both are derivatives 
of the archicoel. Whether, however, a morphological distinc- 
tion can be drawn between the archicoelic coelom of an annelid 
and the gastrocoelic coelom of an Amphioxus, is a question 
which I believe has not yet been considered. 
In regard to the ontogenetic derivation of the blood-vessels, 
or blood lacunae, their endothelia, and the free blood corpus- 
cles, the following points are of interest. These observations 
are based mainly upon data given in the zodlogical text-books 
of Korschelt and Heider, Hatschek, and Arnold Lang. 
In the Nemertini the cavities of the blood-vessels and of the 
rhynchocoel are archicoelic, and these are lined by endothelia, 
from which the floating cells are derived. And, as I have 
shown in a paper, ‘‘On the Connective Tissues and Body Cavi- 
ties of the Nemerteans,” etc., to appear in Spengel’s Zool. 
Jahrb., the gonads and their products are also archicoelic — at 
least in all those forms in which the gonadal sacks are then first 
formed, when the sexual cells become differentiated from the 
somatic cells. 
In the Chaetopoda and the Archiannelida the cavity of the 
blood-vessels is archicoelic, their walls, from which the free 
corpuscles are derived, splanchnopleuric in origin. In the Hir- 
udinea, to cite Korschelt and Heider (p. 222): ‘Von den dor- 
salen und ventralen Blutgefassstammen ist angegeben worden, 
dass sie vom splanchnischen Blatt aus, durch Spaltung dessel- 

