203 



/Nc 



neuroporus and olfactory organ in embryos of chicks, which position 

 V. KuPFFER (4) has confirmed as regards Acipenser. 



The ectoderm is seen considerably thickened and is still connected 

 with the brain in one spot through rows of cells. 



The cells of which 

 the organ consists are 

 generally still round and 

 have the appearance of 

 ordinary embryonic tis- 

 sue but here and there 

 amongst the cells con- 

 necting the organ and 

 brain (Fig. 2 N C) 2i 

 cell may be found that 

 has an elongated form 

 beginning to send out 

 processes. 



The next stage that 

 I have any series of sec- 

 tions from corresponds 

 to that which Ziegler 

 and Balfour call J or 

 K — a longitudinal sec- 

 tion there-of is shewn 

 in Fig. 3. 



Fig. 2. LoDff. sec. through 

 olfactory organ of same emb. 

 250/1. 



It will be seen that the organ has commenced to involute, in- 

 creased in thickness and the basal cells are elongated. The cell-pro- 

 lification is very lively and karyokinesis can be observed in all its 

 stages in many places about the organ. 



The brain has now retracted and is separated some distance from 

 the olfactory organ. 



The connecting elongated nerve-cells are now numerous, sending 

 their processes into the brain or the organ (Fig. 3) and may no doubt 

 be regarded as the first commencement of the olfactory nerve or 

 ganglion. 



Balfour supposes the nerve to grow from the lobe towards the 

 olfactory organ, but it seems more probable that during the process 



