104 DEVELOPMENT OF THE TREMATOD A. 



If this view be correct, which time will determine, it wül be 

 seen that the Bothriocephali, just as all the other animals 

 mentioned in this Essay, which are developed through 

 alternating generations, present quite another and more 

 significant resemblance to plants, than that set up by Prof. 

 Eschricht. The individuals which are fostered by, and 

 appear to proceed from the head by the so-called trans- 

 verse division,* thus attain such a degree of perfection, 

 that the ova are fully formed in them even before they 

 become detached from the "nursing animaV; and, as 

 defensive cases for the ova, they are passed in the natural 

 way from the animal which they have infested, in order 

 probably to reach, eventually, another similar animal, 

 under another form, and as other individuals.! 



* The head of the Bothriocephalus, with all its successive joints, appears 

 to me aptly comparable with the Scyphistoma strobila ; but no one has as yet 

 termed that a compound animal, nor has the term been applied to the 

 connected series of NaidcB, although their condition is a very sinular one. It 

 has been said of all three forms, that they are multiplied by transverse 

 scission or division, expressions which I should not venture to use without 

 prefixing " the so-called," for the relations which obtain in these instances 

 are entirely different from those which would be implied by the separation or 

 abscission of a definite portion of a whole from the other portions of the same 

 whole, in order that the separated portion should itself become another 

 similar whole. I have never been able to meet with Naidce so small, but 

 that it was quite evident that several individuals, iu various stages of develop- 

 ment, were ranged one after the other, and that the one animal was never 

 developed from joints which had previously belonged to another individual. 



f The development which the ova of the Cestoidea undergo must obviously 

 occur under very peculiar circumstances. Professor Eschricht remarks upon 

 this subject, that the ova, collected into masses and encased in a thick 

 sbme or mucus, are passed from the joints packed up, as if they had to 

 make a long and difficult journey. I was also much surprised to see the 

 separate joints of the tapeworm of the sheep and dog passed, each by itself, 

 with the ova, and as it were in a definite proportion with the evacuated 

 faeces ; in a lamb which was much infested "with this worm, I was even struck 

 by the regularity with which each joint of the worm passed through the 

 rectum with four or five balls of the faeces, so that I necessarily concluded 

 that the object of these Httle masses was probably not merely the conducing 

 to the development of the germ in the ovum, but also to the transference of 

 the embryo to new organisms. As matters stand also, I cannot doubt that 

 the Entozoa in certain stages of their growth, or in certain generations, have 

 a geographical extent and distribution in nature (e. g. in water) externally to 

 the organisms which they infest at other times. We could not otherwise 

 easily imagine how the Entozoa of man or of domestic animals, especially in 

 certain races, should occur as they do, dispersed in regions far remote from 

 each other, 



