No. I.] GERM-LAYERS IN CLEPSINE. 147 



that they can easily be seen through the body-wall with the 

 naked eye. What a spectacle is presented when one undertakes 

 to instruct us about the genesis of organs he has never seen ! 

 In his second contribution (No. 23, p. 182) he discovers his 

 error, but charges it to Moquin-Tandon. Has Nusbaum never 

 heard of Leuckart, Leydig, or Claus, that he should go back to 

 an authority of half a century ago to find out how many testiculi 

 Clepsine has? But this is a trivial error in comparison with 

 inaccuracies in observation and reading, such as we shall find in 

 his description of the origin of the nerve-chain, 



Nusbaum (No. 8, p. 21) first attempts to explain why others 

 have been less successful than himself in tracing the derivation 

 of the nervous system. He discovers — so he afiirms — that the 

 egg-membrane is composed of two layers, the inner of which is 

 provided with pores. In the course of development this porous 

 layer is penetrated with vitelline granules, and, sometimes, with 

 protoplasmic particles. " Uou il residte que cette couche pent 

 etre prise assez facilement pour Vectoderme. Alors il doit 

 sembler que le systhne nerveux se forme aux depens du feuillet 

 moyen, de sa couche la plus externe, aboutissanta I'ectoderme," 

 The invention of such a blunder is as preposterous as its com- 

 mission is impossible. Furthermore, such a condition of the 

 egg-membrane as Nusbaum has represented in Fig. 32, PI. III. 

 is either artificial or altogether imaginary. Had Nusbaum be- 

 gun his observations on the germ-bands at an early stage of 

 their development, it would probably never have occurred 

 to him to suspect his predecessors of such a stupid blunder. 

 In these early stages the egg-membrane is not in contact with 

 the germ-bands, and I fail to see how such a strange condition of 

 the membrane could arise. 



In a brief historical review, the opinion which I formerly held 

 (No. i) on the origin of the nervous system is cited as some- 

 thing " strange enough," and as opposed to the ideas of Metsch- 

 nikofif and Hoffmann. I have already made it clear that this 

 opinion coincided with that of Metschnikofif and Hoffmann. 

 Bergh's conclusions on this point are not even mentioned. 



Nusbaum has described the development of the nervous sys- 

 tem in his preliminary article with quite as much detail as in his 

 final paper, and in nearly the same words. I shall, therefore, 

 give here the original description, which runs as follows : — 



