I I 8 TRANSACTIONS OF THE ILLINOIS 



parasites reside in the bodies of insects, even of the same grOTp, without 

 the necessity of this anomalous mode of life ; why, then, is it necessary in 

 the life of the Stylops ? If the male can come forth as a perfect winged 

 insect, why does the female remain a grub? It is possible the reason is 

 to be found in the mode of life of the bee ; but as a species has been 

 found infesting a Homopteroics insect, there would appear to be some 

 other reason. This would appear to be a difficult nut for Sir John Lub- 

 bock and other evolutionists to crack. 



One more illustration and we will close ; but now we leave the insect 

 class and move a little lower down in the scale of animal life. 



There is a group of low, degraded animals, usually quite small, known 

 as Entozoans or intestinal worms, which, though unpleasant objects of 

 study, present some such strange phases of life that I cannot pass them 

 entirely by in this connection. 



In the alimentary canal of certain water-birds is occasionally found 

 a small worm of a peculiar form (shown in the figure), ^which is securely 

 fastened to the walls by minute booklets and sucking disks. Similar in 

 color to the membrane to which it is fixed, without appendages, small in 

 size, and not even worm-like in form, it may easily be taken for some 

 kind of an enlargement of the coats of the intestinal canal ; and few 

 would imagine at first sight that it was an independent or distinct being. 



Like many other species of the group, the two sexes are combined 

 in one individual, hence, in tracing its life, we might reasonably suppose 

 we should have to follow only the one individual. Let us see. 



This produces a few — seven or eight — ova; whether these are hatched 

 before they have passed out of the bird, or afterward, is a part of their 

 history not yet clearly settled; but it is known that immediately after the 

 pseudo-larva leaves the egg it is found in the water. It now resembles a 

 club-shaped fleshy mass (as shown in the diagram), and is surrounded by 

 minute cilia;, by means of which it can move rapidly through the water. 



Although thus active and capable of moving at will, it is, as yet, but 

 little more than an egg, the visible external coat being but a kind of cloak 

 or wrapper for the true embryo within. After swimming freely for a short 

 time in this pseudo-larval state, it attaches itself to the body of some 

 mollusk, as 2. Pahidina, or water-snail. Now the outer envelope drops off 

 and the true larva, which looks more like a bud (represented by the illus- 

 tration) than an animal, appears, but still remaining attached to the mollusk. 

 Gradually increasing in length, it assumes the form represented on 

 diagram, reminding one of a Salamander. 



When it reaches this stage of its life one of the strangest freaks of 

 nature exhibited in the entire animal kingdom takes place. The larva, 

 instead of advancing towards the perfect state, breaks up, as it were, into 

 fragments, each of which is to become a separate individual with a life of 

 its own. In its body cavity a process of gemmation or budding takes 

 place, giving rise to a number of minute bodies, resembling a head of 

 cat-tail with a part of the stem attached (pointing to diagram). These 

 singular creatures effect their escape by bursting through the cavity-walls of 

 the larval parent, or Redia, in which they were developed, causing its death. 



