No. 3] THE TAIL IN LUMBRICULUS. 331 



It has been suggested to me that a parallel exists between 

 the neoblasts and the "islands " of undifferentiated or embry- 

 onic tissue in the larval stages of insects described by van Rees 

 (17). Regions of embryonic cells remain undifferentiated until 

 the close of the larval stage, and then begin their development 

 to form the tissues of the imago. In the same way we find in 

 Annelids a store of reserve material arranged in a very definite 

 manner in response to a special need. 



VI. The Relation of the Observations on the Regen- 

 eration OF LUMBRICULUS TO THE GeRM LaYER ThEORY. 



Without entering into an elaborate discussion of the germ 

 layers, I may point out the fact that the observations on agamic 

 reproduction and regeneration have been cited by a number of 

 writers as subversive of the homology of the layers. 



To give a few instances : Seeliger (19) asserts that among 

 Ascidians the embryological development is not repeated in all 

 its details in the development from the bud. In the bud the 

 wall of the peribranchial space is entodermic in origin, while 

 in the development from the egg it arises from the ectoderm. 



In the buds of Salpa and of Pyrosoma (20) the nervous sys- 

 tem and the wall of the peribranchial space are developed from 

 the mesoderm, while in the embryo they are ectodermic. 



The observations of Seeliger upon the Ascidians show that 

 the mesoblast and chorda of this group have a different origin 

 from that of Amphioxus, and that they are therefore not 

 homologous. 



According to the same author the budding of the Tunicates 

 is not to be harmonized with that of the Bryozoa. Hatschek (8) 

 in 1879 thought that all the germ layers take part in the forma- 

 tion of the bud in Pedicellina. Seeliger, however, has pointed 

 out (21) that ectoderm and mesoderm together give rise to all 

 the organs of the adult, there being a common ectodermic 

 foundation for the atrium, alimentary canal, and ganglion. In 

 a later paper (22) he finds a similar mode of formation of the 

 bud in the Gymnol^emata. More recently the observations of 

 Davenport on Paludicella (4) lead to the conclusion that the 

 two layers of which the bud consists are respectively mesoderm 



