The Microscope. 39 



Fernald and Liidwig have both observed an external layer of 

 small cells surrounding the large cells of the intestine, and Ludwig 

 has discovered beneath the posterior part of the intestine a gland 

 which he thinks is the testis. This is conspicuously developed in 

 some individuals; in others it is not apparent. It is shown in Plate 

 II, fig. 11, c. In those observed by me the length of the gland was 

 about 3 jV 5^ inch. 



12. Chcetonotus tessalatus, Duj. 



I have seen only a passing allusion to this form, and have not 

 had access to the original description. 



13. Chcetonotus hystrix, Metzch. 



The dorsal surface is entirely covered by long recurved spines, 

 which are unequally furcate. Those on the central region of the 

 back are the longest. They decrease gradually in length toward 

 each extremity. I have not met with it. 



14. Chcetonotus spinifer, sp. nov. — Plate II, tigs. 23-27. 



Among Lemna and Riccia from a shallow pond I have obtained 

 many specimens of a well-armored Chsetonotus about j^q- inch 

 long, and having the dorsal and lateral surfaces covered by rounded, 

 imbricated scales, the free margins of which are directed forward as 

 in Ch. loricatus and Ch. rhomboides. From each scale rises a stout, 

 recurved spine whose distal end is unequally and minutely furcate, 

 the base being enlarged and thickened. The arrangement is shown 

 in fig. 27. The spines do not originate from the centre of the scales 

 but from near the posterior part and between the margins of those 

 laterally contiguous. The furcation here, as elsewhere in this kind 

 of appendage, may be described as made by the addition of a minute 

 spur to a curved and simple spine. .It is easily overlooked. The 

 spines are largest and stoutest on the back, decreasing gradually 

 over the neck and head, and rapidly over the posterior parts, while 

 across the dorsal surface immediately in front of the caudal bifurca- 

 tion there extends a supplementary series of four thorns, which are 

 longer and stouter than those on any other part of the body. 



The oral annulus is strongly beaded. The external ad oral cilia 

 form a tuft on each side continued across the ventral surface by a 

 somewhat scattered series. The space between the ventral ciliaiy 

 bands is smooth and naked, except near the posterior extremity 

 where there are five setfe arranged as shown in fig. 23, the most pos- 

 terior two being obscurely furcate; the others are simple setae. 



The oesophagus has on the posterior part of two of the internal 

 margins a thickening in shape like two opposed braces (fig. 24), the 



