286 DE. T. S. COBBOLD ON STKONGTLUS AEKPIELDI. 



uounced intestinal canal, the oesophagus and hind gut being 

 both clearly defined. The mid gut is obscurely cellular in my 

 preserved specimens. Of more interest is the form of the 

 embryo, whose sharp tail supports a distinct, though excessively 

 minute, bristle-like piece at the end. The base of this appendage 

 does not exceed the -2(ruu of an inch in diameter. It may be added 

 that the presence of a small or third spicule in S. Arnfieldi is 

 not distinctive, as I have found a similar arrangement to obtain in 

 S. micrurus, which has hitherto escaped observation. The little 

 piece is about -y^" long in the last-named species. 



In view of diagnosis the following approximate measurements 

 may be found useful. Diameter of the body of the male xi^", 

 of the female yw" ; each large spicule xw" i^ length by about 

 ■^a" broad ; oesophagus of the male j^" long ; anus j-dtj" distant 

 from the end of the tail ; vulva ^" from the point of the tail ; 

 eggs containing coiled embryos -g^" long by -j^^" in breadth ; 

 free embryos j^" in length, and rather less than ■g-jjVo'" i^ 

 breadth ; base of the tail opposite the anus -scVry" broad, and the 

 bristle-like extremity from Yuiiru" ^^ luifnr" o^^J- 



Turning to Strongyhis tetraocmtlius, my object is to contribute 

 a few facts towards a more complete knowledge of the structure 

 and development of this common entozoon. What is at present 

 known of its anatomy is chiefly due to Dr. Schneider. The 

 importance of the worm in relation to the destruction of valuable 

 animals is supreme ; but inasmuch as Sonsino and others have 

 already quoted my published results on this head, I refer those 

 who are interested in questions of parasitic epizooty to some of 

 the papers cited below. I may, perhaps, be permitted to add 

 that an exhaustive knowledge of the human parasitic epidemics 

 can only be obtained by the study of similar outbreaks affecting 

 animals ; and that in both cases any advances made towards 

 combating the evils thereby produced can only rest upon natural- 

 history facts, especially upon those of development. 



On removing full-grown specimens of the four-spined Strongyle 

 from the caecum or colon of any Soliped, their bright red colour 

 at once betrays the leech-like habits of the parasite. Even the 

 perivisceral fluid itself is tinged. The males and females are of 

 nearly equal size, varying from six to eight lines in length. 

 Prof. Schneider has shown that, in addition to the so-called spines 



