418 F. H. Krecker. 



mitotically and amitotically and soon break tlirough the basement 

 membrane into the coelom. 



The participation of ectodermal elements in the formation of the 

 mesodermal stnictures has been repeatedly considered to occur in all 

 annelids thus far studied. Semper in (96) Nais describes a prolife- 

 ration of ectoderm which becomes redifferentiated into mesoderm. 

 Makarofp (99) in Tuhifex, Hepke (97) in Nais, Nussbaum (Ol) in the 

 Enchytraeids, Michel (98) in Lunihrimdus, ÄllolohopJiora and Tuhifex, 

 all claim that the same phenomena occur in these forms. v. Wagner (00) 

 studied Lumhriculus and describes the migration of ectoderm into 

 the coelom and the subsequent formation of mesodermal structures 

 from it. This source of the mesodermal tissues has been denied by 

 Randolph (92), Iwanow (03) and Janda (02). The first two both 

 v/orked on Lumhriculus and Janda studied Rhynchelmis. They ascribe 

 its origin to certain reserve cells known as neoblasts. These are deri- 

 vatives of the Peritoneum and are unusually large oviTm like cells of 

 irregulär outline. The nucleus fills most of the cell and it is normally 

 circular, the greater portion of it being occupied by a central clear area 

 in which no bodies appear except a large nucleolus, the chromatin 

 bodies being confined to the periphery of the nucleus outside of the 

 clear space. The cytoplasm is capable of amoeboid movements, at 

 times sending out branched pseudopodia, and the nucleus also changes 

 its shape (Fig. 9). In what may be termed the resting condition these 

 cells are attached to the septa in the ventral half of the body only, on 

 both sides of the nerve cord, sometimes singly at other times in groups 

 of two or three, rarely more (Fig. 11). Randolph (92) found them 

 "in every somite of Lumhriculus with the possible exception of one or 

 more at the anterior extremity" but v. Wagner (00) does not find 

 them so widely distributed in this form, usually none at all in the 

 anterior 12 to 18 somites. Neither have I noticed them in every somite 

 of Tuhifex and Limnodrilus. In but two or three instances have I 

 observed them in the dorsal half of the body. Less frequently they 

 are found along the blood vessels or between the chlorogogue and the 

 intestine. During regeneration from the posterior end of the body 

 several of them are found at this point. The severing of the body 

 apparently acts as a Stimulus which causes them to leave tlieir 

 places of rest and migrate to the wound. The part which they play 

 in regeneration has caused considerable discussion. 



Senlper in a description of budding in the Naids was the first to 

 pay them much attention. Since he found them in the midventral 



