DEVELOPMENT OF PHRYGANIDS. 597 



this supposition improbable. It is more likely that it had 

 some sensory (?) function on account of the peculiar structure 

 and development of the ectoderm cells, while at the same time 

 the longitudinal duct leading into a cavity into which the large 

 cells could pour a secretion points to the supposition that it is 

 possibly of a glandular nature. 



In Blatta the heart is formed by the fusion of mesodermic 

 folds similar to those in Phryganids; instead, however, of 

 forming a solid cord the heart is from the first hollow. The 

 mesodermic folds pulsate regularly long before they have 

 united to form the heart. 



Note. 



Since the completion of this paper on Blatta and Phryganids 

 the work of Dr. A. Korotneff on the development of the heart 

 in Gryllotalpa has appeared {' Zool. Anzeizer/ December 24th, 

 1883), which contains several points on the origin of the heart 

 and blood-corpuscles resembling what I have found in Blatta. 

 The blood-corpuscles both in Blatta and Phryganids are formed 

 from free mesoderm cells, which, however, do not arise in the 

 median line of the embryo, as this author has indicated, but 

 from the apex of the angle made by the united splanchnic and 

 somatic mesoderm. 



The condition shown in Gryllotalpa, in which the semicircular 

 projections on the uprising mesodermic folds are formed before 

 the folds have hardly begun to grow towards the back, is not 

 attained in Blatta until the folds have very nearly united with 

 each other in the median dorsal line. Moreover, a thin layer 

 of mesoderm always closes in the yolk dorsally before the 

 mesoderm folds unite, thus preventing a communication between 

 the blood system and the yolk-sac, as Tichomerof has described 

 in Lepidoptera. 



I cannot believe that the condition represented by Korotnefi" 

 is possible. In the first place it is improbable, on theoretical 

 grounds, that a blood sinus should be formed simply between 

 the vitelline membrane and the yolk, as he described. In fact, 



VOL. XXIV. NEW SER. S S 



