TiENIA ECHmococcus. 255 



cannot fail to suggest important hints as to the best mode of check- 

 ing that formidable endemic known as the Echinococcns disease 

 of Iceland, the best account of which we owe to the researches of 

 Eschricht. Before, however, I enter systematically upon the sub- 

 ject of hydatids it is necessary for me to say a few more words 

 respecting the structure and development of the adult tapeworm 

 which gives rise to these formations. 



In many particulars this species differs from the other cestodes 

 we have considered, but the more noticeable of these variations 

 have reference to the form and disposition of the reproductive 

 organs. If the lowermost segment be examined, it will be seen 

 to exhibit the usual central uterine rosette, and an equally con- 

 spicuous intromittent organ which is often protruded. The rela- 

 tion of these parts to the other sexual elements is seldom fairly 

 seen, but their connection has been tolerably well made out by 

 Yon Siebold and Leuckart, from whose writings, aided by specimens, 

 one may gather a tolerably correct notion of their disposition. The 

 essential male organ consists of numerous testicular sacs, commu- 

 nicating (by the intervention of numerous seminiferous ducts) with 

 a common vas deferens. These sacs are sparsely scattered over 

 the lower part of the segment, and present the appearance of 

 small pyriform bodies. The vas deferens is very much twisted 

 upon itself before it enters the cirrhus-pouch ; the latter being 

 very largely developed. According to Leuckart, one not unfre- 

 quently sees the extremity of the penis bent round and inserted 

 into the commencement of the vagina, constituting, in point of 

 fact, the act of coitus. If his views are correct, the proglottides 

 are thus self-impregnating, but I must confess that I am sceptical 

 on this point. Thus, supposing Leuckart is right, one naturally 

 asks such questions as the following : — Why need there be so large 

 a development of the penis and its pouch ? Why is the surface 

 of the former as well as that of the lining membrane of the vagina 

 furnished with such a formidable array of spines ? Why is the 

 intromittent organ so constantly seen protruded at the margin of 



