368 Mr Cobb, On Free-living fresh-water 



If one possesses and uses a slide rule or other calculating 

 machine the labour of producing the formula from such a skeleton 

 is much reduced. I estimate that in most cases by the above 

 method the formula may be derived from a specimen in about five 

 minutes, provided there is a clear perception beforehand of what is 

 to be done. 



Where the worm is of large size, too large for measurement 

 under the microscope, the camera lucida may be mounted on a 

 lens holder without any lens, in which case the worm may be drawn 

 natural size or even be reduced. 



The rules etched upon glass so that the scale can be laid in 

 contact with the paper, thus doing away with parallax, are very 

 convenient for use in measuring the skeleton drawings. 



Mermis Novae Zealandiae, n. sp. 



•0 1-7 4-7? '48-' 26 ? 



■1 t -6 1~ ! 28 ' *° 38 ' mm - 



is the best formula derivable from the half dozen specimens 

 examined, only one of which was beyond question adult. The 

 thin, smooth, whitish, translucent skin is destitute of hairs and 

 striae, and it would appear that the musculature is weak. The body 

 is threadlike and uniform in diameter, and ends anteriorly in a 

 neck which in its anterior half is slightly convex-conoid. The 

 head end is truncate, apparently without papillae, and certainly 

 without setae, lips, lateral organs and eyes. There is no proper 

 pharynx, the pore-like mouth opening being continued in the 

 oesophagus as a tube of the same diameter. The cylindrical 

 oesophagus is two-fifths as wide as the neck and in all the 

 specimens is somewhat indefinite, though the length given in the 

 formula is believed to be at least approximately correct. The 

 intestine was plainly visible in most parts of the body but was 

 manifestly becoming obsolete. No anus was to be seen. The 

 posterior extremity for a distance equal to two to three body widths 

 was more transparent owing to the absence of intestine. No 

 ventral gland was seen. 



The nerVe ring was not very satisfactorily located but the 

 measurement given in the formula is probably fairly correct. 



The tail is rather suddenly convex-conoid at the somewhat 

 blunt terminus, and it is quite destitute of hairs or papillae. 

 There are no caudal glands and no spinnerets. The body con- 

 tinues to have its usual width until within a short distance of the 

 tail end, the tapering taking place in a distance no greater than 

 two to three times as great as the width of the body. The 

 inconspicuous vulva is located very slightly in front of the middle 

 of the body. There are two uteri, extending in opposite di- 

 rections. In the only gravid female seen they contained towards 



