262 



with earlier authors in showing that alimentary tract and nervous 

 system are both derived from this inner layer , but I did not suppose 

 that this was sufficient proof that there was larval entoderm in the 

 inner layer, which was the point at issue. I did not suppose, in fact, 

 that one was justified in concluding that the cells going into the 

 middle layer of the bud are neither ectoderm nor entoderm from ob- 

 serving their fate. 



After calling attention to the previously known fact that the ma- 

 terial of the inner bud layer is derived not from the larval ectoderm 

 but from the region of the lips of the blastopore — the ect-ental 

 region — I felt justified in drawing the conclusion which might natu- 

 rally have occurred to any one under the same circumstances, that 

 these cells are neither ectoderm nor entoderm only secondarially be- 

 coming differentiated. I do not think, however, that Bra em had ex- 

 pressed this idea or that I may justly be accused of having appropriat- 

 ed his ideas without due credit. 



3. The difiierence between Brae m' s idea and mine may be given 

 in two quotations; the first column is taken from his work (1890, 

 p. 29); the second from mine (1891, p. 72). 



Sämmtliche Knospen der Co- There is in every stock of 



Ionie gehen auf einen begrenzten Bryozoa a mass of indifi'erent cell 



Complex embryonaler Zellen zu- 

 rück, welche aus dem Material 

 des Statoblasten oder des Eies 

 ursprünglich erübrigt und von 

 Knospe zu Knospe weiter- 

 geführt wurden. 



material, which is derived directly 

 from indifi'erent cells of the larva 

 or embryo, and whose function is 

 to form the organs of the various 

 individuals including the polypi- 

 des. This indifi'erent cell material 

 lies in the body wall , principally 

 at the growing tip or margins of 

 the stock. By its growth and dif- 

 ferentiation it gives rise to the 

 body wall, muscles, etc., and at 

 intervals it leaves behind 

 as a portion detached from 

 itself, a mass of indifferent 

 cells, which is capable of 

 forming a polypide, or of 

 becoming a new centre of 

 growth or of both. 

 I further added (1891, p. 72) : «This hypothesis diff'ers from that of 

 Braem in that the pre-existence of a Knospenanlage assumed by 

 B r a e m is , according to my view a non-essential feature in the for- 



