598 WILLIAM PATTEN. 



I do not believe such an extended space as he described exists 

 at allj unless produced by shrinkage due to reagents. The yolk 

 is separated from the vitelline membrane by the upgrowing 

 mesoderm folds, and the only space formed is just before the 

 folds unite to form the heart, and this space is simply the cavity 

 of the heart. 



The primitive blood sinus is not the space between the lips 

 of the mesoderm folds, however large or small this may be, for 

 this space is not in communication with the body cavity at all, 

 and even when the mesodermic folds first begin to beat the 

 space contains no blood-corpuscles. The primitive blood sinus, 

 then, is the space between the somatic and splanchnic meso- 

 derm, divided into a number of smaller and irregular sinuses 

 by meshes of connective tissue, some cells of which, in the 

 earlier stages, become free and form the blood-corpuscles. By 

 the pulsation of the mesodermic folds, long before a special 

 heart is formed, a circulation through the irregular sinuses of 

 the body cavity is brought about, like the circulation in many 

 of the lower Worms. 



By the union of the mesodermic folds a definite heart is 

 formed, from whose walls, in the earlier stages, a number of 

 blood-corpuscles are produced in addition to those formed in 

 the true body cavity. I hope to produce absolute proof of this 

 statement, accompanied by drawings of cells in different stages 

 of separation from the dorsal inner wall of the heart, when all 

 my observations onBlatta are completed and published. These 

 facts add the evidence of embryology to that of comparative 

 anatomy, to show that the heart of Worms and Arthropods is 

 a comparatively new structure, which was preceded by a circu- 

 lation produced by contraction of the muscular walls of the 

 body cavity. 



