THE EMBRYOLOGY OF THE APTERYGOTA. 



AGNES M. CLAYPOLE, Ph.D. 



Up to within the last few years comparatively little work has 

 been done on the embryology of the lowly insect forms included 

 in Brauer's group Apterygota, and until we reach the recent date 

 of 1892 no studies of serial sections have been reported. Hence 

 there are among earlier works many misinterpretations of super- 

 ficial features. Much of the early work was done on members 

 of the subdivision Collembola, including the more lowly aptery- 

 gote insects. The first contribution came from the system- 

 atist Nicolet. Unfortunately, but meager data of this article 

 have been obtained. It can merely be stated that some time 

 previous to 1869 Nicolet published studies on Podura aqiiatica, 

 Desoria cineTea, Cypiiodeirus agilis, Sviiiithuriis ornahis, and 

 Onhesella sp(.'). He established three facts : that holoblastic 

 cleavage exists among the Collembola; that their eggs are 

 spherical ; that an amnion and serosa are wanting. 



In 1 87 1 Packard! gg^ye the results of studies on the form 

 Isotoma zvalkcri, not a thysanuran, but a collembolan. Only 

 the stages after germ-band formation are mentioned. This is 

 said to arise as a complete girdle and to show early 6-"] seg- 

 ments. These were identified as antennae i, mandibles i, 

 maxillae i, with possibly a second, thoracic legs 3. Later rudi- 

 ments of a spring appear on the fifth abdominal segment ; an 

 unpaired median labrum is also developed. At no time are any 

 tracheae present, and the larvae on leaving the egg resemble the 

 lower Collembola more than the adult Isotoma. A cuticle like 

 that of crustaceans appears during development. 



In 1875 Oulganine^ published studies on Achonites tubercu- 

 latus Nic, AnuropJiorus fimetariiis, and two species of Degeeria. 



1 Packard, Jr., A. S., " Embryological Studies on Diplax, Perithemis, and the 

 Thysanurous Genus Isotoma," Peabody Acad. Sci. No. ii. 1871. 



2 Oulganine, \V., " Sur le Ueveloppement des Podurelles " (Extrait du Russe par 



M. de Korotneff), Arch, de Zool. Expcr. Tome iv. 1875. 



