308 SYNOPTIC COLLECTION. 



The segments of the adult are obscured, the secondary 

 annular markings obliterating the division lines of the 

 true segments. Paddles and setae are not developed in 

 Hirudo, the animal either swimming by means of the thin 

 edges of its body or crawling by aid of its suckers. It 

 is, however, a sluggish creature, so that it often remains 

 attached by its suckers for a long period of time. 



Hirudo may be a descendant of the land leeches, like 

 Haemadipsa ceylonica. The fact that its eggs are laid in 

 earth above water-mark would indicate such a descent. 



This is probably the case with another fresh-water 

 leech, Clepsine (No. 764 ; PI. 765, fig. i), which is a fish 

 parasite. 1 Although the eggs of this leech are not laid in 

 cocoons, yet they are covered after attachment to some 

 water plant, with a fluid that soon hardens and which 

 serves for protection. The parent covers the eggs with 

 her body and also carries the young about with her 2 until 

 they are old enough to care for themselves. The devel- 

 opment illustrates, according to Whitman,3 ontogenetic 

 concentration in which the earlier phases of one stage 

 appear before the later phases of the preceding stage are 

 completed. It is in a worm with this accelerated develop- 

 ment that we find the segments of the body distinct in 

 the young and indistinct in the adult. PL 765, fig. i, is 

 a drawing of Clepsine when seven days old and when it 

 has nearly attained the form of the adult. The internal 

 organs of a species of Clepsine (C. compJanatn) are well 

 shown in fig. 2, which is a dissection that has been treated 

 with reagents. The portions colored pink and blue con- 

 stitute the sacculated digestive system which begins at the 

 mouth and ends in the rectum (see figs, i, 2). The dark 

 red organs are the excretory organs or nephridia which 

 are in pairs (fig. 2). 



1 Whitman, Quart. Journ. Micr. Sci., XVIII, 1878, p. 224. 



2 Whitman, loc. cit., p. 225. 



3 Loc. cit., p. 272. 



