264 BNTOZOA. 



these structural characters, the endocyst is sometimes denominated 

 the cellular layer. 



One of the most interesting physiological questions suggested 

 by the peculiarity of these organisms, is that which has reference 

 to the mode of development of the scolices, or so-called Bchino- 

 coccus heads. Until very recently, this problem has not been 

 satisfactorily solved ; and even now, there are, of course, minor 

 differences of opinion. The generally-received notion that the 

 heads bud out stoloniferously, as it were, is altogether disproved ; 

 whilst the more ingenious views promulgated by Huxley are, I fear, 

 almost equally iacorrect. 



To render a clear account of the history of the formation of the 

 Echinococci it is necessary for me to remind the reader that the 

 older authors supposed that in course of development the heads 

 became detached from the endocyst, and escaping into the fluid 

 interior of the cavity, swam about vigorously. Some, including 

 Professor Owen, averred that these movements were brought about 

 " by means of superficial vibratile cilia;" and many more supposed 

 that their ulterior stages of development were completed whilst 

 they were thus enjoying a free and active mode of existedde. The 

 stern realities of recently-discovered facts require us to dismiss all 

 these, and many other equally incorrect views. Whether we have 

 to do with simple isolated hydatids, or whether we have to deal 

 with compound exogenous, endogenous, or multilocular formations, 

 the developmental process is essentially the same in aU cases, at 

 least, in its main features. I shall now, therefore, give a brief 

 description of the process, chiefly in accordance with the views 

 promulgated by Leuckart, finally quoting from the same authority 

 his own account of the variations of opinion which subsist between 

 himself ^nd other authorities. 



The first indication (of what is subsequently to become an 

 Echinococcus head, or a group of heads) consists of slight papilli- 

 form elevation at the inner surface of the endocyst. This promi- 

 nence — ^which does not hitherto appear to have been recognized in 



