574 TEXT-BOOK OF ENTOMOLOGY 



arise by two paired invaginations of the lateral walls, forming a 

 split at their bottom. 



The rudiment of the heart stands, as we have seen, in intimate 

 union with the primitive segments. Out of the lateral walls of 

 these segments, after giving off the elements of the somatic meso- 

 derm, arises an epithelial plate which becomes the rudiment of 

 the pericardial septum or dorsal diaphragm (Figs. 523, A-C, dd, 

 544-545, ps). As soon as the two halves of the rudiments of the 

 heart have united with each other in the dorsal middle line, the two 

 halves of the pericardial septum unite with each other and form 

 the wall to the pericardial cavity and shut it off from the rest of 

 the body-cavity. For a long time the pericardial septum remains 

 in union with the wall of the heart. Afterwards, however, it sepa- 

 rates from it (Fig. 523, C, dd). (Korschelt and Heider.) 



The statements of other authors (Ayers, Grassi, Patten, Tichomeroff, Car- 

 riere, Heider, Heymons, etc.) as to the mode of origin of the heart in insects of 

 other orders are all similar to the type described in Gryllotalpa. The difference 

 consists mostly in the fact that the two large blood-lacunse are wanting or only 

 exist to a slight extent. It results that the rudiment of the cavity of the heart 

 in the earlier stages is of slight extent and often scarcely recognizable. 



In CEcanthus (Ayers) and in Gryllotalpa, the hinder section of the heart 

 is the first to develop, the development advancing from behind forward. 



The blood-corpuscles. Blood-cells are said by Korotneff to be, in 

 Gryllotalpa, at an early period present almost everywhere between 

 the yolk and mesoderm; they are derived, as he states, from the cells 

 of the somatic mesoderm layer, which has lost its connection with the 

 other parts of the mesoderm, and fall into the body-cavity. Ayers 

 states that the blood-corpuscles arise from serosa nuclei which have 

 passed into the body-cavity, where they become more vesicular, 

 and ultimately all of the nuclear substance goes to form from one 

 to three spherical bodies, which are surrounded by the common 

 membrane. 



"These bodies are blood-corpuscles and are free nucleoli imme- 

 diately on the rupturing of the vesicle which surrounds them." 

 (Ayers, PI. 22, Figs. 1, 3, p. 250.) More recently, Schaeffer has 

 observed in caterpillars certain cell-complexes associated with the 

 fat-body which he has called blood-forming masses. 



Musculature, connective tissue, fat-body. The muscles of various 

 parts of the body, as well as the connective tissue, arise by histo- 

 logical differentiation from the somatic layer of the mesoderm 

 (Fig. 523, so). The fat-body originates from the same source, as 

 shown by the researches of Kowalevsky, Grassi, and of Carriere. In 



