20 
Psyche 
March 
come together and their nuclear membranes break down 
where they are in contact with each other (Fig. 8). At the 
same time the chromatin of each condenses into a fine 
spireme. The nuclear sap of the female pronucleus simul- 
taneously develops an affinity for light green, so that the two 
pronuclei can no longer be distinguished. The spiremes of 
the two nuclei become coarser and intermingle before any 
distinct chromosomes are visible (Fig. 11). The maturation 
divisions occupy about one and one-half hours each. Union 
of the pronuclei occurs during the fourth hour after ovi- 
position. 
Affinities of Lepismatids 
The lepismatids for which both embryological and mor- 
phological data are available are Lepisma saccharin a L. 
(Heymons, 1896, 1897; Uzel, 1897, 1898), Thermobia do- 
mestica (Packard) (Woodland, 1952, 1957; Sahrhage, 1953; 
Wellhouse, 1953), and Ctenolepisma lineata Fabricius 
(Woodland, 1957). All three belong to Subfamily Lepis- 
matinae. The data indicate that Thermobia domestica and 
Ctenolepisma lineata are very closely related to each other 
and less closely related to Lepisma saccharina, which is more 
primitive than they. 
Thermobia domestica and Ctenolepisma lineata differ 
embryologically from Lepisma saccharina in that in them 
the germ disk is formed at the extreme posterior end of the 
egg, radial symmetry is maintained until the germ disk 
starts to elongate, the embryo does not sink bodily into the 
yolk, the amniotic pore is not closed by a chitinous plug, and 
spiracle anlagen are not found on the ninth and tenth ab- 
dominal segments. Adults of Thermobia domestica and 
Ctenolepisma lineata differ from those of Lepisma saccha- 
rina by lacking parameres and by possessing ventricular 
caecae, an anterior projection of the vas deferens beyond 
where the most anterior pair of vasa efferentia empties into 
it, and often a third pair of styli. In the former two species 
the vasa efferentia of the members of a pair of sperm tubes 
do not unite before joining the vas deferens and the free end 
of one member of each pair of sperm tubes is directed 
mediad, while the free end of the other member is directed 
laterad. In addition, the lateral oviducts are relatively 
