544 ALFRED C. H ADDON. 



diverticula and a simultaneous arrest in the formation of the 

 permanent alimentary canal. The following diagram (fig. 5) 

 will sufficiently explain my meaning. This would make the 

 hody-cavity of these forms an enterocoel. The musculature of 

 the body-wall appears to develop prior to the formation of 

 these diverticula. 



This author brings into harmony the observations of Allman, 

 Metschnikoff and Nitsche, for we have only to concede that 

 the epithelial lining of the body-cavity of the embryo (cystid) 

 in my interpretation of AUman, (which, by the bye, was made 

 before I had seen the accounts by Nitsche and Reinhardt), is 

 derived from archenteric diverticula ; an earlier or later deve- 

 lopment of the tunica muscularis between the two layers, is 

 really of little consequence. 



Fig. 5. — Diagram representing a possible degradation in tlie formation of the 

 alimentary tract from an originally enterocoelous larva. 



Salensky (9) states that his own observations on Paludi- 

 cella have convinced him that the superior layer of the 

 zooecium gives rise to the lophophore and the internal epithe- 

 lium of the polypide, while the 'inferior layer is transformed 

 into the interior layer of the zooecium, the tentacular sheath, 

 and, at the same time, into the muscles. He says (p. 56): — 

 " It is impossible not to remark the interesting analogy exist- 

 ing between these two layers and the embryonic layers of other 

 animals." . . . . " It is acknowledged by several recent 

 embryological researches that the cndoderm of many animals 

 forms from the ectoderm, sometimes as a thickening of this 

 latter, sometimes as an invagination." 



This '* analogy," wliich otlier autliors liave remarked, must 

 not be relied on as giving any true insight into the nature of 

 the phenomenon of budding, for we cannot look upon the 

 epiblastic layer of the endocyst as being morphologically 



