310 ANIMAL PARASITES. 



the body of the mother (for example, in the Filarice), and partly 

 outside the uterus of the female worm. The latter, again, may 

 occur within the body of one and the same host, which may, pro- 

 bably, very seldom or perhaps never be the case ; or, as usually 

 happens, outside the body of the previous host in the open 

 waters. That the latter is a very general occurrence we know 

 from the investigations of Verloren and Richter. 



In the early part of the month of August, 1853, Verloren 1 

 put a fragment of a mature female Ascaris marginata of the dog 

 into water, so as to preserve the eggs in the water by the pre- 

 vention of evaporation. Of these he examined specimens from 

 time to time under the microscope. The segmentation of the 

 vitelli and the development of the young immediately com- 

 menced. In about fourteen days the process was completed, and 

 perfectly developed young worms made their appearance; these 

 moved briskly within the egg-shells, but did not break through 

 them, as Verloren expected, from similar successful experiments 

 by Schubart. With the decrease of temperature towards 

 autumn and winter, the mobility of the embryos within the egg- 

 shells also diminished, until at last it entirely ceased in the 

 winter, but recommenced in the following spring, and again 

 became very distinct in the summer months. During the whole 

 course of the experiment a spontaneous exclusion of the em- 

 bryos from the eggs never took place. In these eggs, therefore, 

 the following remarkable peculiarities may be observed. The eggs 

 of other animals may, indeed, lie for a long time before the young 

 make their appearance; as, for example, in many insects, but 

 this always takes place within a year ; the eggs of many animals 

 may also be delayed for a long time in their development, but 

 then the development of the young cannot have commenced at 

 all. But if this be once the case, and the young be developed, 

 it must either be excluded soon, or it dies in a few days ; 

 whilst, in the present instance, the ready formed embryo lives 

 more than a year in the egg-shell, like other worms in an 

 encysted state, which live enclosed in their cyst. Both are, 

 probably, enabled to live for a certain time unchanged in the 

 egg-shells or cysts, both, as is well known, agreeing in being 



1 Aanteekingen van het verhandelde in de vergadering der Seotie voor Natur en 

 Geneeskunde van het Provinciaal Utrechtsch Genootschap van Kunsten en Wetens- 

 chappen, Gehonden den 9 Septembre, 1854. 



