DEVELOPMENT. 195 



accessory reproductive glands have also a tegumentary origin. 

 In the female Cockroach the chitinogenous epithelium of the 

 integument gives rise to the uterus, vagina,* and accessory 

 glands, the muscular and connective tissue layers of the sexual 

 apparatus being formed out of loose mesoblastic cells. f 



JOSEPH 



Post- embryonic Development. 



At the time of hatching the Cockroach resembles its parent 

 in all essentials, the wings being the only organs which are 

 developed subsequently, not as entirely new parts, but as exten- 

 sions of the lateral edges of the thoracic terga. The mode of 

 life of the young Cockroach is like that of the adult, and 

 development may be said to be direct, or with only a trifling 

 amount of metamorphosis. In the Thysanura even this 

 small post- embryonic change ceases to appear, and the Insect, 

 when it leaves the egg, differs from its parent only in size. It 

 is probable that development without metamorphosis was once 

 the rule among Insects. At present such is by no means the 

 case. Insects furnish the most familiar and striking, though, 

 as will appear by-and-by, not the most typical examples of 

 development with metamorphosis. In many text-books the 

 quiescent pupa and the winged imago are not unnaturally 

 described as normal stages, which are exceptionally wanting in 

 Orthoptera, Hemiptera, Thysanura, and other " ametabolous ' 

 Insects. It is, however, really the " holometabolous ' Insects 

 undergoing what is called " complete metamorphosis," 

 which are exceptional, deviating not only from such little- 

 specialised orders as Thysanura and Orthoptera, but from nearly 

 all animals which exhibit a marked degree of metamorphosis. 

 "We shall endeavour to make good this statement, and to show 

 that the Cockroach is normal in its absence of conspicuous 

 post-embryonic change, while the Butterfly, Bee, Beetle, and 

 Gnat are peculiar even among metamorphic animals. 



* Genital pouch of the preceding description. 



f Indications, which we have not found time to work out, lead us to think that 

 the development of the specially modified segments and appendages in the male and 

 female Cockroach needs re -examination. We hope to treat this subject separately 

 on a future occasion. L. C. M. and A. D. 



