THE REPEODUCTION OF ANNELIDS. 869 



nate generation, he dwells particularly on the striking differences 

 between the males and females, and says, the only link now wanting is 

 to trace the development of an embryo coming from the ovum of one 

 of the female individuals into a parent stock, similar to that from 

 which the sexual individual was produced, which should in its turn, 

 produce males or females only by division and not by sexual repro- 

 duction. It was this link which Mr. A. Agassiz has been fortunate 

 enough to discover. Before proceeding to notice this portion of 

 the subject, we wish to call attention to the fact tbat an important 

 paper* by Professor Huxley on a fissiparous species of tubicolar annelid 

 is forgotten in the otherwise admirable resume of this part of the 

 subject. In this annelid, which has been provisionally assigned to 

 the genus Protula, the prolification appears to take place so as to 

 separate all the segments of the parent behind the sixteenth, as a 

 new zooid ; but it is not a mere process of fission, for the seventeenth 

 segment, i.e. the first of the new zooid, undergoes a very considerable 

 enlargement, and eventually becomes divided into the nine segments 

 of the head and thorax of the bud. These segments do not appear all 

 at once, but gradually, one behind the other. The intestinal canal 

 of the stock and of the bud are at first perfectly continuous, but the 

 peri- intestinal cavity of the bud is completely filled with a mass of red 

 granules. These would seem in some way to subserve the nutrition of 

 the young animal, for in some free zooids, apparently fully formed, but 

 wanting the sexual organs, the caudal segments were full of them, 

 while no trace of them was to be found in the anterior segments. 

 From a consideration of the various modes of proKfication described 

 by O. E. Miiller, Milne Edwards, Schulze, and others. Professor 

 Huxley enumerates the following different forms. 



1. All the segments of the zooid form mere segments of the 



* parent stock,' the new products being merely cephalic organs. 



2. None of the segments of the produced zooid belonged to the 



* parent stock,' but the former is a metamorphosis of a whole segment 

 of the latter. 



3. None of the segments of the produced zooid belonged to the 



* parent stock,' and the former contains hardly any of the primitive 

 substance of the latter, being developed by germination from its last 

 segment. 



The prolification of the Pro tula described by Professor Huxley, 



* Edinburgh New Philosophical Journal, Vol. I. n. s. 1855. p. 113. 

 N.H.R.— 1865. 2 C 



