190 EMBRYOLOGY OF INSECTS AND MYRIAPODS 



periphery before and after the formation of the blastoderm and gathering 

 in a ball of cells in the center of the egg are said by Uzel (1898) to be 

 entodermal. The mid-gut epithelium arises from bipolar rudiments, 

 augmented by cells from the middle strand, in Isotoma (Philiptschenko, 

 1912). 



The germ band in Lepisma and Campodea is formed by a migration of 

 cells to the ventral side where the band develops. In Isotoma the entire 

 blastoderm first acquires an inner layer. Later the inner layer breaks 

 down on the sides, leaving a broad strip of inner-layer cells in the dorso- 

 ventral circumference interrupted only between the future head and tail 

 where the primary dorsal organ is formed. With Macrotoma the first 

 anlage of the germ band appears in the form of four blastoderm thicken- 

 ings which will develop into the head lobes and the mandibular segment. 

 The germ band in Isotoma, Anurida, and Campodea is very long, extending 

 nearly around the egg periphery. At blastokinesis the embryo reverses 

 its position, bringing the dorsal side to the surface by a buckling process 

 (Figs. 79, 84, 107), as in Geophilus. This type of reversal occurs also in 

 Macrotoma. In Lepisma and Machilis the very short germ band sinks 

 into the yolk with formation of a sort of amnion and serosa. 



The abdomen of Campodea in the embryo as well as in the adult is 

 composed of 10 distinct segments, in addition to the anal plates. In the 

 young embryo of Lepisma there are 1 1 abdominal segments in addition to 

 the anal plates. In older embryos of Macrotoma but 6 abdominal seg- 

 ments may be counted in addition to the minute anal plates. Rudiments 

 of appendages develop on the intercalary (premandibular) segment in 

 Campodea. At first postoral in position, as are also the antennae, they 

 later migrate forward. 



References 



Collembola: Achondes armatus; Uzel (1898). Anurida maritima; Claypole 

 (1898, 1899), Folsom (1900), Ryder (18866). Anurophorus laricis; Lemoine (1883). 

 Entomobrya (Degeeria) spp.; Uljanin (1875). Hypogastrura purpurascens; Strebel 

 (1932). Isotoma sp.; Packard (1872). /. cinerea; Philiptschenko (1912). /. grisea; 

 Prowazek (1900). /. walkerii; Packard (18716). Neanura muscorum {Achondes 

 tuherculatus);\J\]a,nm (1875). Orychiurus {Anurophorus) sp.;V\\a.nu\ (1875). Podura 

 sp.; Barrois (1897), Uljanin (1875), Weismann (1882). Sminthurides aquaticus; 

 Falkenhan (1932). Sminthurinus aquaticus; Strebel (1932). S. niger; Strebel (1932). 

 Sminthur us sp.; W Signer (1900). *S. /wscms; Lemoine (1883). Tetrodontophora gigas; 

 Heymons (18966). Tomocerus plumbeus; Hoffmann (1911). T. vidgaris; Uzel (1898). 



Aptilota: Thysanura; Bekker (1927), Brandt (1878), Uzel (1897a, 1898). Caynp- 

 odea sp.; Grassi (1886). C. staphylinus; Uzel (18976, 1898). Japyx solifugus; 

 Grassi (1886). Lepisma saccharina; Heymons (18966, 18976, 1905). Machilis 

 alternata; Heymons (1905). 



