360 MONTGOMERY. [VoL. XII. 
cavity of the heart is archicoelic. In Peripatus (2dzd., p. 711), 
the heart is formed by mesodermal cells, its cavity being arch- 
icoelic. The blastocoel of the Myriapoda (zézd., p. 752) becomes 
filled with yolk, while later mesodermal cells penetrate and sur- 
round the yolk, producing a pseudocoel ; these cells accomplish 
the formation of the blood-vessels, and perhaps also of the 
heart. The body cavity of the Insecta is a product of the 
primitive archicoel and the coelom ; the heart is formed of mes- 
odermal cells of protovertebral origin, and the blood corpuscles 
are also of similar derivation (zézd., pp. 818, 833, 834). 
In the Mollusca the archicoelic (pseudocoelic) body cavity : 
“stellt im Allgemeinen das Lacunen- und Sinussystem des 
Korpers dar, in welches sich die Arterien 6ffnen, und aus 
welchem die Venen, wo solche vorhanden sind, ihr Blut bezie- 
hen. Sie ist ohne eigene Epithelwand”’ (Lang, p. 792). The 
true coelom is much reduced, being represented only by -the 
pericardial and gonadal cavities, and is bounded by its own epi- 
thelium. The blood-vessels (a closed system only in the Ceph- 
alopoda and certain Prosobranchs) have no endothelium (Lang, 
p. 780). In the Lamellibranchiata, the heart, aortae, and gill- 
veins are produced by the agency of mesodermal cells in the 
primitive body cavity ; there is no communication between the 
blood-vessels and the pericardial cavity (Korschelt and Heider, 
pp. 971, 973). The heart in the Gasteropoda is derived from 
the pericardium, while “die Gefasse entstehen als Liickenraume 
im mesodermalen Zellmaterial der primaren Leibeshohle (Blas- 
tocoel), also zunachst ganz unabhangig vom Herzen” (zdzd., 
pp. 1081, 1082). In Phoronis a coelom is well developed and 
is bounded by an endothelium (Lang, p. 213). The blood-vessels 
probably arise as lacunae in the splanchnopleuric mesoderm : 
‘‘wahrend nach Cori das Gefasssystem des ausgebildeten Thieres 
ein vollstandig geschlossenes ist, scheint in der Larve eine Com- 
munication zwischen demselben und dem Kopftheil der Leibes- 
hohle zu existiren. Im letzteren sollen die Blutkérperchen in 
Massen angehauft ihre Entstehung nehmen” (Korschelt and 
Heider, p. 1184). 
In the Ascideae, the early coelomic cavities give way later 
to a mesenchym, which fills the archicoel: “die spater in die- 
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