SECTIONAL TRANSACTIONS.—D. 458 
simple alternating cycle. Subsequent stages in evolution comprise complete 
loss of sexuality, migration, and morphological changes through natural selection 
in a second environment, evolution of a return migrant, and recent acquirement 
of long-lost sexuality through individuals with few characters in common with 
other individuals of the cycle, and a final recapitulation of the original cycle on 
the definite host-plant. 
22. Dr. H. A. Bayuis.—Some Considerations on the Host-range of 
Parasitic Nematodes. 
The nematodes parasitic in vertebrates show great variety in the extent to 
which they are limited to particular hosts. A review of a considerable number 
of genera shows that they may be divided broadly into a section with more or 
less strict ‘ specificity’ and a section with members occurring in various hosts, 
often of quite distantly related groups. 
Many of the genera with wide ranges have an intermediate host (commonly 
an invertebrate) during their earlier phases, and it is suggested that these 
forms, being introduced into the final host at a more advanced stage than those 
which have a direct development, are better able to withstand violent changes 
of environment, and thus better able to adapt themselves to a variety of final 
hosts. 
Since ‘ specificity ’ can only be rightly considered in its relation to evolution, 
it is suggested that among forms with a direct development those which show 
the strictest specificity are the most specialised, this being often correlated 
with specialisation, in habits or otherwise, of the hosts, while those which 
_ have a wide range have retained a primitive adaptability. 
23. Discussion on The Systeniatic Position of the Nematoda, opened 
by Prof. S. J. Hickson, F.R.S. 
24, Prof. B. Buackiock.—The Tumbu Fly, Cordylobia anthropophaga 
Griinberg, and the Congo Floor Maggot, Auchmeromyia 
luteola. Fabricius, in Sierra Leone. 
The Tumbu Fly is a troublesome fly in tropical regions of Africa on account 
of the habits of its larve. ‘lhese enter the skin of animals and proceed to grow 
and develop there until the larve are full-grown and ready to pupate, when 
they leave the skin and continue their development on the ground. Man and 
many animals are affected by them, and suffer from painful boils as a result 
of the presence of the larve in the skin. Young animals are very heavily 
infected and frequently die as the result of the disease. It has been possible 
to obtain large numbers of wild and laboratory-bred flies, and as a result a 
study of the various stages from egg to adult has been possible. Many new 
facts on the morphology of the stages and on the bionomics have been observed, 
and it has been determined that wild rats are an important factor in the 
preservation and spread of the infection. 
; The Congo Floor Maggot is a parasite which has a totally different life- 
history. This maggot’s unique habit of sucking blood from human beings lying 
asleep on the floor of their huts was discovered by Dutton, Todd, and Christy 
in 1904 while on an expedition of the Liverpool School of Tropical Medicine to 
the Belgian Congo. This larva is incapable of penetrating the skin, but it 
has a special arrangement of the mouth apparatus by which it is enabled to 
adhere firmly to the skin while sucking blood. 
The adult flies of the two larve are similar in appearance and belong to the 
same sub-family Calliphorine of the Muscide. A comparative study of myiasis 
due to these and other larve is outlined. 
25. Mr. H. Granam Cannon.—On the Post-naupliar Development oj 
an Estherid Crustacean. 
The post-naupliar development of an Estherid Crustacean from Baghdad has 
been worked out. The larva hatches as a true nauplius. The mesoderm of the 
_ post-naupliar region forms a continuous sheet around the gut, This very early 
_ splits along the mid-dorsa] line, thus forming the cardiac cavity. Ventrally 
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