THE MUSCULATURE, CONNECTIVE TISSUE, AND FAT-BODY. 341 



Iii Gryllotalpa and Oceanthtis (Ayees) the posterior portion of the heart 

 develops first. .The order of development of the heart is here from behind 

 forward. This is an unusual condition, which is due to the fact that the closing 

 of the dorsal region is retarded by accumulated masses of yolk in the anterior 

 part of the body. 



[As in Gryllotalpa, the heart in Agelastica (Petrunkewitsch, No. XXXVI.) 

 and Bombyx (Tichomiroff, No. 78) is formed by the circumcrescence of the 

 yolk by the mesoderm-bands. When these reach the mid-dorsal line, the two 

 layers fuse immediately below the ectoderm, while they remain distinct below ; 

 in this way a mesodermal groove arises which, owing to the fact that the ento- 

 dermal epithelium is still incomplete dorsally, is in open communication with 

 the yolk. This constitutes the gastro-vascular canal of Tichomiroff, which, 

 in transverse section, has the form of a figure 8. At this stage the dorsal and 

 lateral walls of the heart are formed by mesoderm, while the incomplete ventral 

 Avail is entodermal. The entodermal epithelium now unites in the middle line, 

 and thus completely separates the heart from the enteron and, soon after, the 

 mesoderm grows in from either side towards the middle line below the cavity of 

 the heart and above the entoderm, and finally, by fusion of the two ingrowths, 

 the mesodermal walls of the heart are completed. The closure of the heart 

 takes place earlier at the anterior and posterior ends than in the middle. — Ed.] 



The blood-corpuscles are traced back by Korotneff to cells of 

 the somatic mesoderm which have lost their connection with the 

 rest of the mesoderm and have passed into the body-cavity. Our 

 own researches incline us to agree with this statement. Other 

 authors, however (Dohrn, and recently Will also, No. 97), have 

 derived the blood-corpuscles from yolk-cells. A vers (Xo. 1) even 

 claims for their formation the cells set free by the disintegration of 

 the [dorsal plate. It should here be pointed out that Schaffer 

 {Xo. 124a) recently maintained that certain cell-complexes connected 

 with the fat-body in caterpillars are formative centres for the blood- 

 •corpuscles (p. 372). 



H. The Musculature, the Connective Tissue, and the 



Fat-body. 



The groups of muscles, as well as the connective tissue, are derived 

 through histological differentiation from the somatic layer of the meso- 

 derm (Fig. 167, to). Our own researches, and those of Kowalevsky, 

 Grassi, and Carriere, show that the fat-body also arises from the 

 mesoderm. In Hydrqphilus, a dorsal band-like fat-body, running over 

 the intestine, arises by direct transformation from the wall of the 

 coelomic sac. For the rest of the fat-body also, for instance, for the 

 lobes accompanying the tracheal system, a mesodermal origin can 

 be indisputably established. The observations made by Heymons 

 on Phyllodromia are in harmony with this. Certain cells of the 

 wall of the coelomic sac early undergo a transformation, which 

 results in their being recognisable as the rudiment of the future 

 fat-body (Fig. 169 B and G, /). 



