122 
Parasitic Arthropoda 
the batch was then placed at 70° F. for one night, near a white 
rat. The next day all the cocoons were empty and the fleas were 
found on the white rat. 
Thus, temperature greatly influences the duration of the pupal 
period, which in Ceratophyllus fasciatus averages seventeen days. 
Moreover, when metamorphosis is complete a low temperature will 
cause the imago to remain within the cocoon. 
Sexually mature and ovipositing fleas, he fed at intervals and kept 
alive for two months, when the experiment was discontinued. In 
the presence of rubbish in which they could bury themselves, unfed 
rat fleas were kept alive for many months, whereas in the absence of 
any such substratum they rarely lived a month. In the former case, 
it was found that the length of life is influenced to some degree by the 
temperature and humidity. In an experiment carried out at 70° F. 
and 45 per cent humidity, the fleas did not live for more than four 
months, while in an experiment at 6o° F. and 70 per cent humidity 
they lived for at least seventeen months. There was no indication 
that fleas kept under these conditions sucked moisture from surround¬ 
ing objects, and those kept in bell jars, with an extract of flea-rubbish 
on filter paper, did not live any longer than those which were not so 
supplied. 
Curiously enough, although the rat is the normal host of Cerato¬ 
phyllus fasciatus, it was found that when given the choice these fleas 
would feed upon man in preference to rats. However, none of the 
fleas laid eggs unless they fed on rat blood. 
The experiments of Strickland on copulation and oviposition in 
the rat flea showed that fleas do not copulate until they are sexually 
mature and that, at least in the case of Ceratophyllus fasciatus, the 
reproductive organs are imperfectly developed for some time (more 
than a week) after emerging from the pupa. When mature, copula¬ 
tion takes place soon after the fleas have fed on their true host—the 
rat—but not if they have fed on a facultative host only, such as man. 
Copulation is always followed by oviposition within a very short, 
time. 
The effect of the rat’s blood on the female with regard to egg- 
laying, Strickland concludes, is stimulating rather than nutritive, 
as fleas that were without food for many months were observed to 
lay eggs immediately after one feed. Similarly, the male requires, 
the stimulus of a meal of rat’s blood before it displays any copulatory 
activity. 
