116 EMBRYOLOGY OF INSECTS AND MYRIAPODS 



in Scolopendra by Heymons (1901), of Carausius by Wiesmann (1926), 

 of Locusta by Roonwal (1937) and others are given in Part II. 



DEFINITIVE BODY CAVITY 



After the degeneration of the walls that separate the longitudinal 

 row of coelomic sacs, converting them into a coelomic tube, one on each 

 side of the median line, some investigators state that an open communica- 

 tion is established between the coelomic lumen and the epineural sinus. 

 This is said to occur in Hydrophilus, Blatta, Forficula, and some chryso- 

 meUds, among them Donacia, according to Heider (1889), Cholodkowsky 

 (1891), Heymons (1895&), Lecaillon (1898), and Hirschler (1909), respec- 

 tively. In Carausius Wiesmann (1926) found that an actual opening 

 between the coelomic cavities and the epineural sinus did not arise but 

 that, instead, thinning of the inner coelomic wall occurred which would 

 permit diffusion of the haemolymph. The coelomic cavities are little 

 by little obliterated by the conversion of the walls of the sacs into a fat 

 body and muscle anlagen excepting only that the ampullae of the ducts 

 of the reproductive organs are retained. Indirectly, then the coelomic 

 sacs contribute to the formation of the body cavity of Carausius as in 

 other insects. The definitive body cavity, therefore, may be considered 

 a mixocoele. Paterson (1932) likewise states that in the chrysomelid 

 beetle, Euryope, there is no direct communication between the coelomic 

 cavities and the epineural sinus, which is in agreement with McBride's 

 (1914) observation that an opening between coelomic cavity and epineural 

 sinus is contrary to what is known of the later development of the coelom 

 in other animals. All authors, however, agree that the first anlage of the 

 definitive body cavity is formed independently of the coelomic cavities. 

 Some writers state that the epineural sinus is formed by the retraction 

 of the yolk from the inner surface of the germ band. This occurs in 

 Carausius after the formation of the first anlage of the mid-gut epithelium, 

 and Wiesmann (1926) is inclined to the opinion that this is what takes 

 place in other animals also. On the other hand, Roonwal (1937) says 

 that in all insects except the Acrididae it is at first not delimited dorsally, 

 i.e., on the side of the yolk, by a membrane. In the Acrididae this sinus 

 at the time of its first appearance is bound dorsally by a membrane as in 

 Stenohothrus and Locusta. It should be mentioned that a similar mem- 

 brane has recently been described by Scholzel (1937) as occurring in the 

 head louse and by Miller (1939) in the stone fly. 



During the growth of the embryo of Locusta the epineural sinus 

 becomes enlarged and forms the definitive body cavity which is then the 

 haemocoele. With the conversion of the walls of the dorsal coelomic 

 pouches into fat, etc., the coelomic cavities also merge into the epineural 



