POWEE OF SPONTANEOUS DIVISION. 261 



spermatic particles, has long recognized the existence of separate sexes* ; 

 and long before this, Stannius had concluded that the sexes were sepa- 

 rate, from the fact that in different individuals the contents of the 

 general cavity of the body were different f. Stannius also observes 

 that the parent sperm- cells leave the segmental organs (his testes) 

 before the formation of the spermatozoa, which are found only in the 

 cavity of the body. Krohn, Frey, and Leuckart assert that the ova and 

 spermatozoa are developed free in the general cavity of the body. 



(673.) In relation to the spontaneous division of the Annelida, Dr. 

 Williams observes : It is true that, towards the latter end of every 

 summer, certain species of worms are multiplied by a cutting across the 

 body at one or more points. If the fissure occurs at more than one 

 point, the animal, of course, becomes divided into more than two pieces. 

 This circumstance seldom happens. The fissure in Arenicola generally 

 occurs somewhere within the middle third of the body, securing a few 

 branchial tufts for each fragment. The tail, however, is sometimes 

 detached, and sometimes the division happens very near the head. 

 This process, in Arenicola, happens during July and August. The ce- 

 phalic and caudal pieces continue for some time to writhe in the sand, 

 somewhat further down in the soil from the surface than the perfect 

 individuals. Towards September, the fragments (both that attached to 

 the head and that belonging to the tail) dissolve away, ring by ring, and 

 finally disappear by decomposition. If the fragment examined be that 

 of the tail, it will be observed at the point of separation to exhibit an 

 eversion of the edges, placing the alimentary canal exteriorly ; and a 

 very evident increase of size in the vessels also occurs, accompanied by 

 a tumefied state of all the structures of the part. From this latter fact, 

 it is easy to be misled into the idea that the vessels can become enlarged 

 for no other purpose than that of repairing the injury done by the 

 fissure, or, perchance, of reproducing the part detached by that process. 

 Such would naturally be the meaning which a physiologist would attach 

 to the swollen appearance of the blood-vessels. But such is not the 

 conclusion to which the careful practical observer is conducted by the 

 study of the actual phenomena of the process. It is, of course, in- 

 disputable that nature accomplishes some adequate object by the fissure 

 of the body of the worm ; but that_object, whatever else it be, is unques- 

 tionably not that of multiplying the species. The tail-fragment never, 

 as can be proved by easy observation, produces a single new ring or 

 segment of the body. If this be true, how completely improbable must 

 be the statement that the headless piece is capable of producing a new 

 head ! In Arenicola, Dr. Williams can confidently declare that such 

 reproductive properties as those implied in the re-formation, and that 

 too by a remnant of an integral part of the body, do not exist. It is 

 equally inaccurate to maintain that a new tail is formed by the cephalic 

 * Comptes Eendus, xvi. 1843. t Miiller's Archiv, 1840. 



