13 



are of a yellowish color, have an operculum, and are found in 

 vast numbers in individual specimens of the entozoon. Slides 

 Nos. 2 and 3 exhibit the eggs as taken from the uterine tube, 

 and on slide No. 3, near some of the eggs, are to be seen some 

 spermatic filaments. 



Alternate generation is the term applied to the various 

 transformations these entozoa undergo in the course of their 

 full development. There is a missing link in some of the 

 stages, but sufficient is known for a thorough comprehension 

 of the subject. The eggs being formed by the elaborate and 

 beautiful reproductive system above described, escape from the 

 uterus one at a time, and when perfectly mature the operculum 

 is pushed off by the energetic action of the ciliated embryos 

 within. An examination of slide No. 3, will show embryos 

 (unfortunately not sufficiently advanced to exhibit cilia) 

 amongst the extruded vitellus. In some cases these embryos 

 make their escape whilst the egg is within the uterus, but 

 more frequently they escape whilst the egg lies on the marshy 

 or moist pastures. According to Siebold the development of 

 the egg is as follows : — " After the disappearance of the ger- 

 minative vesicle, large transparent embryonic cells appear in 

 the midst of the vitellus, which undergo fissuration. These 

 multiply by division, increasing at the expense of the vitellus, 

 which in the end they completely replace. When this has 

 taken place there is a mass of extremely small cells, which 

 being covered with a delicate epithelium having cilia, form a 

 round or oval embryo." The ciliated embryo can progress in 

 moist grass or water, and, sooner or later, attaches itself to 

 the surface of the body of some mollusk, most commonly the 

 limneus, planorbis, or paludina, when it loses its ciliated 

 epithelium and gains access to the interior of its host. When 

 there the germ bud contained in the embryo developes rapidly 

 into a non-ciliated larva, within which another family is 

 developed. The enlarged larva is now transformed into a cyst, 

 and is then called a " nurse," and its contained family develope 

 into cercariae. These cercarise have an independent life of their 

 own, and it is not absolutely necessary to their existence that 

 they should enter the viscera and liver of a vertebrate, but when 

 there, they meet their highest form of development in the 

 mature liver entozoon. I regret much that I have not been 

 able to prepare specimens of the cercariae, but when I do so 

 I will forward some for inspection. 



Let us recapitulate these powers of reproduction, commenc- 

 ing with the full-grown fluke : — In each individual a vast 

 number of eggs are matured, and each one of these eggs 

 contains a ciliated embryo, capable, after entering a moUus- 

 cau host, of developing into a non-ciliated larva j this larva 



