W. Nicoll 
147 
Temnocephala. Practically nothing of very great moment has been 
done on the development of the Cestodes apart from the already 
mentioned work of Young (1908) on histogenesis in Cysticerci, and of 
Child (1907) on the development of the germ cells in Moniezia. 
Perhaps the most interesting detail in life-history is the discovery of 
further cases of fleas acting as intermediate hosts of tape-worms. The 
new observations were made by Dampf (1910) and Nicoll and Minchin 
(1911). Altogether four cases are now known, namely, the dog tape¬ 
worm (Dipyliclium caninum), the rat tape-worm (Hymenolepis diminuta), 
and two others of which the adult forms are not definitely known. 
The most important work on Nematode development is without 
question that of Looss (1911) on the human hook-worm ( Agchylostoma 
duodenale). In a very exhaustive monograph he has dealt with 
practically all the points of importance in the life-history of this 
exceedingly formidable parasite. It is impossible to refer in detail 
to all the questions discussed by Looss, many of which, indeed, have 
a wide bearing on the general subject of Nematode development. The 
most vital facts are that the larva of this worm can enter its host by 
penetrating the unbroken skin, and that in the life-cycle there is no 
heterogenesis or double sexual cycle. The original statement of both 
these facts dates from an earlier period than we are considering here, 
but they have been so seriously criticised during the intervening years 
that only now can they be regarded as having received absolutely 
irrefutable confirmation. Another classical Nematode, of which the 
life-history has been established, is the Guinea-worm ( Dracuncidus 
medinensis). We owe our knowledge of the life-history of this worm to 
the researches of Fedtschenko, Graham, and most recently, Leiper (1906). 
In the last place mention must be made of the very considerable amount 
of general cytological and developmental work which has been done 
upon Ascaris, the most outstanding being that of Zur Strassen (1906) 
and Martini (1906). 
There remain for consideration several scattered observations on the 
bionomics of parasitic worms in general. Of these only a few can be 
mentioned here. Some interesting notes were made by Jarnmes and 
Martin (1908, 1909 and 1910) on the conditions of development of 
Nematode eggs. They found that the egg-shell is practically im¬ 
permeable, except to gases, at ordinary temperatures, but when the 
temperature' is raised the impermeability is modified and several 
substances such as hydrochloric acid, sodium carbonate, etc., are able 
to permeate. They also found that Nematode eggs may be classified 
