Hog Lung-Worms 207 
tioned, into any region of her hody, so that they penetrate to the uterus. 
Here the sperms are discharged and fertilization takes place. 
The females are viviparous and produce hundreds of young. Within 
the uterus the eggs may be found in all stages of development. This 
development becomes more and more complete as the eggs approach 
the oviduct, till finally, when this last is reached, full grown, active 
larvae may be seen coiled within the egg capsules. The eggs are oval 
in shape and possessed of at least two membranes. On the outside there 
is a thick envelope of a gelatinous nature, which is very sticky, and which 
adheres readily to whatever surface it touches. Around the body of 
the embryo there is another thin, protective membrane, within which 
the embryo may often be found intact, even after the removal of the 
outer gelatinous coat. The thin, transparent, membranes which sur- 
round these eggs, together with their ease of procurement, should 
make them ideal for the study of karyokineses, and kindred biological 
investigations. 
‘The body wall of these parasites shows many peculiarities. En- 
closing the body contents is a transversely striated, muscular layer, 
somewhat thickened at the two extremities. In the male, well defined, 
oblique striations occur in the region of the bursa. The costae which 
support the bursal membrane are projections of this same muscle layer. 
On the outside there are several layers of very thin cornein, which are 
transparent and easily permeable to gases and liquids. When an adult 
specimen is placed in distilled water, the following changes may be 
observed: In a few minutes the outer layer of cornein separates from 
the muscle layer in blister-like swellings all over the body. These 
blisters are very transparent and easily overlooked. When touched 
with a needle, they at once collapsed, showing that they are formed 
of a membrane which encloses a fluid of high osmotic pressure. As 
this interchange of liquids continues, the specimen grows tense and 
turgid, until it finally bursts open along the median ventral line. The 
body contents are then forcibly ejected by the contraction of the longi- 
tudinal muscle fibres in the body wall. The rupture thus begun con- 
tinues throughout the whole length until the worm is entirely everted. 
In this condition the body wall looks like an undulated band or ribbon, 
» and is shrunk to about one-fifth of its original length. Specimens 
prepared in this manner are easy to study as the internal organs suffer 
little injury. By this means the eggs are discharged in great abundance 
wherever suitable conditions are found. 
The characteristics shown by these worms suggests at once that 
very exact environmental conditions are necessary for their development. 
In this phylum of parasitic roundworms, respiration is seemingly effected 
through the dermal surface, for the adults, at least, show very quick 
responses to density changes in surrounding liquids. Indeed, so delicate 
is this adjustment, that a specimen of Trichinella spiralis (which had 
been kept in strong formaldehyde solution for three years) exhibited 
very life-like movements, when placed into a drop of water. Other 
specimens, known to be dead, acted in like manner when the solution in 
which they were kept, was placed upon a slide, and allowed to evaporate. 
These experiments would tend to prove that the body wall plays an 
