ECTODERMAL DERIVATIVES 95 



covered these structures, which he considered part of the stomatogastric 

 nervous system, in the walking stick. Carriere and Burger (1898) found 

 that in the mason bee (Chalicodoma) the gangUa allata have the same 

 origin as in Forficula, but these bodies do not later fuse to form a median 

 body as they do in Forficula. They remain attached to the ventrolateral 

 margins of the antennal coelomic sacs, as in the honeybee (Nelson, 1915). 

 These authors expressed a doubt whether or not these bodies consisted of 

 nerve tissue. They have since been termed the corpora allata and proba- 

 bly are glandular in function. According to Roonwal (1937) the corpora 

 allata of Locusta migratoria arise in the stage soon after blastokinesis as a 

 pair of invaginations of the lateral body wall of the embryo on either side 

 of the intersegmental region between the mandibular and the first maxil- 

 lary segments. The bhnd ends of these invaginations are directed medio- 

 dorsally. They soon become rounded and are eventually severed from 

 the outer ectoderm. Later this structure moves dorsally and posteriorly 

 and comes to lie on the stomodaeum. Its connection with the stomato- 

 gastric nervous system is purely secondary. Its thin mesodermal coat 

 arises from the antennary coelom, as in Carausius (Wiesmann), and not 

 from the mandibular coelom, as Heymons claims for Carausius (Bacillus) 

 rosii. 



The corpora allata are ectodermal in origin according to most writers 

 who have investigated the matter. In Forficula (Heymons, 1895) they 

 appear to arise as ingrowths from the anterior angle of the maxilla, a pair 

 of rounded bodies becoming constricted off and eventually finding their 

 way to the antennary coelomic sacs, to the lower ends of which they 

 attach themselves. This appears to be the case also in Chalicodoma 

 (Carriere and Burger, 1898), Formica (Strindberg, 1913), Apis (Nelson, 

 1915), and Pieris (Eastham, 1930a). In Silpha (Smreczynski, 1932) and 

 Coryrodes (Paterson, 1935) they likewise originate near the base of the 

 mandibular segment or between this and the maxillary segment. In 

 Calandra oryzae, however, according to Tiegs and Murray (1938) they 

 arise from the antennary segment; and though they form in intimate 

 association with the tentorium, they are, as far as could be ascertained, 

 purely a differentiation of the ventral wall of the antennary coelomic 

 sac; i.e., they are mesodermal. 



THE TRACHEAL SYSTEM 



The first evidence of the formation of the tracheal system is the 

 appearance of small ectodermal pits, or invaginations, along the sides 

 of the body. These pits deepen into tubes which subsequently fork out 

 into branches. The branches subdivide repeatedly, becoming finer and 

 finer. In the beginning each invagination acquires at its blind end two 

 diverticula of which the posterior one fuses with the anterior of the next 



