22 
Psyche 
March 
ment. In Thermobia a distinct pause occurs after differen- 
tiation of the first 5 abdominal (first 8 post-cephalic) seg- 
ments. The cercus-bearing (pre-anal) and anal segments 
are prominent during the interval before the remaining 
abdominal segments are differentiated in front of them. 
The characters in which Hanseniella differs from Ther- 
mobia may be grouped into several categories. Examples of 
characters with homo'ogs in some primitive or generalized 
insects, but not in Thermobia , are: (1) Paired arteries 
arise from the aorta. (2) The presence of eversible sacs 
and coxal styli. Homologs of both of these structures are 
present in Machilis. In Hanseniella the two halves of the 
nerve cord arise laterally from the floor of the germ band 
rather than medially as in Thermobia. In Hanseniella the 
medial position is occupied by the “ventral organs” from 
which the eversible sacs arise. Examples of characters 
more primitive than those found in primitive insects are: 
(1) The adult has abdominal legs. (2) Only one pair of 
Malpighian tubules is present. (3) The labial segment is 
at first not part of the head. A few of the characters of 
Hanseniella , such as the secondarily acquired progoneate 
condition and the development of fat body from yolk cells, 
seem to express affinity with diplopods or as the incorpora- 
tion of a pre-antennary ganglion into the brain, with chilo- 
pods. Other characters of Hanseniella, as the absence of 
eyes and the presence of only a single pair of tracheae 
(cephalic), are specializations which are probably adapta- 
tions to its environment of decaying foliage and rotting 
logs. 
The following embryological differences between Han- 
seniella and lepismatids are considered by the author to be 
the result largely of the difference in relative volume of yolk 
in their eggs. In Hanseniella : (1) Cleavage is total (2) 
The germ band is long and from the beginning represents 
thoracic and abdominal as well as cephalic material. (3) 
Absence of embryonic membranes ; the germ band does not 
sink into the yolk. (4) Early eclosion, with subsequent 
anamorphosis. Actually nutritive value of the yolk rather 
than volume is concerned here. Information is not available 
on this subject in insects. 
