156 CONVERGENCE IN MINUTE STRUCTURE 



the oesophagus is suppressed, the outward differ- 

 entiation of the stomach is lacking, and there 

 is no pylorus and no pyloric cceca. So again, 

 continuing our analysis, we find that flame-cells 

 or solenocytes, nematocysts, myoepithelial cells, 

 spicule-forming cells, ganglion cells, pigment cells, 

 striated muscle cells, etc., may be regarded as 

 belonging to the category or repertory of the 

 primary constituent elements of animal tissues, 

 and will appear when required to fit in with 

 a special set of physiological conditions. Let 

 us imagine a limited number of primary physio- 

 logical conditions of excretion. Some or all of 

 these conditions will recur independently in each 

 of the phyla of the animal kingdom. To meet 

 them, the necessary cellular elements, till then 

 held in abeyance, will be forthcoming. 



Bewildering as may be the striking identity 

 which Goodrich has established between the 

 solenocytes of Amphioxus and of Polychaetes, it 

 is perhaps not more remarkable in principle than 

 other cases of identical anatomical differentiation, 

 some of which have been referred to in the 

 preceding chapters. 



As might have been expected, this case of 

 nephridial convergence has been hailed with 

 delight by Dr Gaskell, who looks upon it as 

 an acceptable confirmation of his deductions. I 

 may be permitted to make the following quota- 

 tion from his book, whilst at the same time 



