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tion of the structure and function of the intestine of the Isopods is 

 discussed, and in which the author feels himself obliged to criticize 

 my arguments 2 as to the non-digestive function of the '"midgut". In 

 doing so he would be quite within his rights and if it were simply a 

 question of criticism, I should find nothing objectionable. But un- 

 fortunately Herr Schönichen has not only misunderstood my line 

 of argument, but has misrepresented my statements in a most remark- 

 able manner. Errors in deduction are possible for everyone, but to 

 conduct such a line of argument as Herr Schönichen attributes to 

 me would betray a weakness of intellect such as I do not care to be 

 held responsible for. 



A word is necessary as to the embryonic origin of the "midgut". 

 Herr Schönichen, basing his faith in histological data, claims for 

 it an endodermal origin, calmly dismissing the embryological evidence 

 as to its ectodermal nature advanced by Dohrn, Bobretzky, Nuß- 

 baum and myself^, because Reinhard has maintained that it is 

 endodermal. The ectodermal origin is easily demonstrated and un- 

 mistakable, and the opinion of the majority in this instance is un- 

 questionably correct. 



1 may take this opportunity of recording an observation as to the 

 manner of elongation of the proctodaeal invagination in Oniscus. In 

 the examination of series of longitudinal sections of embryos I found 

 karyokinetic figures in the wall of the invagination only in a narrow 

 zone situated immediately behind its anterior extremity. It seems 

 probable that the elongation takes place, similarly to that of the ecto- 

 derm and mesoderm of the metanaupliar region of the body, by the 

 division of pole cells, which may be termed proctoblasts, and, if so, 

 the arrangement of the cells of the adult intestine in longitudinal rows 

 receives a simple explanation. 



Herr Schönichen writes as follows: "... muß McMurrich, 

 wenn der Mitteldarm nicht verdauen soll, den Sitz der Verdauung in 

 den Kaumagen verlegen. Vom Kaumagen aber ist, wie schon oben 

 erwähnt wurde , ein ectodermaler Ursprung völlig sichergestellt. 

 McMurrich kommt also mit seinem ersten Einwand vom Regen in 

 die Traufe". It is hardly fair to suppose that anyone would be so 

 foolish as to advance the ectodermal origin of a portion of the intestine 

 as an objection to its being regarded as digestive in function if the 

 only other region in which digestion could take place were also ecto- 

 dermal. Herr Schönichen overlooks the fact that his is not the only 



2 The Epithelium of the so-called Midgut of the Terrestrial Isopods. Journ. 

 of Morph. XIV. No. 1. 1897. 



3 Embryology of the Isopod Crustacea. Journ. of Morph. XL No. 1. 1895. Herr 

 Schoenichen does not appear to have known of the existence of this paper. 



i 



