340 



INSECT A. 



connected and bound the 

 pericardial space, which 

 is closed towards the 

 rest of the body-cavity 

 (Fig. 172, ps). For a 

 time the pericardial sep- 

 tum remains connected 

 with the wall of the 

 heart, but it becomes 

 separated from it later 

 (Fig. 167 C, dd). The 

 relations of the rudi- 

 ment of the heart and 

 the pericardial septum 

 to the terminal filament 

 of the genital rudiment 

 will be discussed below 

 (p. 345 et seq.). 



The statements as to the 

 development of the heart in 

 the Insecta that have heen 

 made by other authors 

 (Grassi, Patten, Ticho- 



MIEOFF, AYERS, HeIDER, 



Carriere, Heymons, etc.). 

 can easily be traced back 

 to the type described for 

 Gfryllotalpa. The principal 

 difference in the formation 

 consists in the absence or 

 slighter development of the 

 large blood-lacunae above 

 described. The rudiment 

 of the heart in the first 

 stages is consequently of 

 small extent, and can often 

 hardly be recognised. 



Fio. 167. — Diagrammatic transverse section through three consecutive stages of GryUotalpa to 

 illustrate the formation of the dorsal vessel (after Korotxeff). (The rudiment of the fibrous 

 layer of the intestine is omitted in these diagrams). A, youngest stage. The germ-band 

 extends from *x to y*. The embryonic envelopes are rent and retracted dorsally. am, edge 

 of the rent ; rp, dorsal plate (serosa); /, lamella connected with the ectoderm of the germ- 

 band (amnion reflected back). B, second stage. The germ-band has almost completely 

 grown over the food-yolk. The dorsal organ is absorbed. C, third stage, dorsal region. 

 The formation of the heart is completed, am, vestige of the amnion-fold; bs, blood-sinus; 

 dd, rudiment of the dorsal diaphragm ; dc, ventral diaphragm ; do, food-yolk ; dz, yolk-cells ; 

 ec, ectoderm; gr, vascular channel (rudiment of the heart); 7, lamella of the reflected 

 amnion; Ih, permanent body-cavity; ru, transverse muscle; n, ventral cord; r, heart; rp, 

 dorsal plate ; sp, splanchnic, so, somatic layer of the mesoderm ; its, cavity of the primitive 

 segment; *x-y*, lateral termination of the germ-band. 



