and the Embryology of Autolytiis cornulus. 395 



small cirrus (c), as in the female; but when the animal is 

 seen from below, as in PI. XI. fig. 8, we notice an addi- 

 tional, still smaller cirrus [c'") which is entirely wanting in 

 the female, as well as the small tentacular cirri {a"') (PI. 

 IX., fig. 7), which are found at the base of the tentacles 

 {a' and a") on the upper side of the head. The large dor- 

 sal cirri of the first ring are usually carried slightly curved 

 back at the extremity (PI. XI. fig. 8, c'). Tlie needle-shaped 

 bristles are somewhat longer than those of the females ; oth- 

 erwise neither these nor the hooked bristles differ in any way 

 in the two sexes. The alimentary canal, in both the males 

 and females, is narrower while it passes through the ante- 

 rior rings (/), which have only stout bristles, widening sud- 

 denly as it reaches the rings where the setae begin {/'). 



Besides these two sexes differing to such an extraordi- 

 nary extent, there is still a third kind of individual (PI. 

 X., fig. 1), which is neither male nor female, never has 

 either eggs or spermatozoa developed, and differs more 

 from the males than they differ from the females, and 

 yet belongs to this same species. In fact, these indi- 

 viduals are the parent stocks, as I have called them 

 above, from which are developed by transverse division 

 males and females (PL IX., fig. 9). We cannot call this 

 mode of reproduction a case of budding : it is the develop- 

 ment of a head and all its appendages, either male or 

 female, and the gradual addition of a very small number 

 of rings, between this head and the tail-ring, which was at 

 first a part of the parent stock, and remains the tail-ring 

 of the male or female after it has separated from the 

 parent stock ; a large portion of the original parent stock 

 becoming separated, to form part of individuals which 

 alone have the power of developing eggs and spermatozoa, 

 this power being entirely wanting in the parent stock. 

 We have here, therefore, an actual case of alternate gen- 



