396 On Alternate Generation of Annelids, 



eration, just as much as in the case of the " Strobila ;^' an 

 individual entirely different from the males or females, from 

 which are developed, by a peculiar mode of transverse 

 division, those very males and females which have sper- 

 maries and ovaries. These eggs, as I shall show below, 

 instead of developing into males and females, are trans- 

 formed into these parent stocks; which produce in their 

 turn individuals having sexual organs, by transverse divis- 

 ion, and never any thing else. During a whole summer I 

 have had daily a large number of these worms alive ; and 

 have traced individuals raised, from the eggs until they 

 reached the condition of the parent stock, upon which I 

 was observing the growth of the males and females. 



The parent stock (PI. X., fig. 1) has the same color as 

 the males and females. The tentacles of the head are 

 like those of the female, the middle tentacle being longer, 

 however; while the first ring instead of being consolidated 

 with the head, as in the males and females, is distinct from 

 it, and on each side of it we find two cirri, one long one 

 (C), and a short one ( O") in advance and below it. The 

 second ring has a long dorsal cirrus ( C') on each side, cor- 

 responding to the cirrus c' of the males and females. The 

 third ring has a shorter dorsal cirrus ( C") of the length of 

 the cirrus O". The succeeding rings all have cirri, 

 diminishing in length as they recede from the head, until 

 near the tail, which has two large cirri, where they are 

 hardly perceptible. In place of the large, highly-developed 

 eyes of the males and females, we find two large and two 

 small eyes, which are mere accumulations of pigment cells. 

 The larger eye is placed below in advance of the smaller, 

 and is nearer the edge of the body, the small eyes being 

 quite close together (PI. X., fig. 1, O). The rings are 

 provided only with one kind of bristles, the short stout 

 ones, exactly like those of the males and females (PI. IX., 



