The American Xatiiral'tHt. 



Of the subsequent fate of the embryo to the time of its hatching in 

 the adult form we can only note from the detailed organogeny given 

 by the author the facts that the reproductive organs arise from two 

 small sets of cells given off from the progeny of I, that is from the 

 entoderm : that the nervous system and muscles both come direct from 

 the ectoderm, the former as solid ingrowths, the latter as sinking in 

 of separate cells, muscle cells. The excretory tubes arise from cells of 

 undetermined origin. The flame cells are from the first blind tubes, 

 closed by a protoplasmic mass bearing the numerous cilia. 



The author also takes up, in less detail, the embryology of Melictm 

 ringens, a less favorable subject. Here also the precaution was taken 

 to keep the observed embryos up to hatching to avoid the vitiation of 

 results by study of abnormalities. 



The cleavage is remarkably similar to that of Callidina. Yet the 

 polar body is found towards the posterior, dorsal end. 



Both male and female eggs have the same cleavage and subsequent 

 development in spite of difference of size. 



In the author's interpretation of the embryology of Rotifers there is 

 no mesoderm, no middle layer. The sexual organs arise from the 

 entoderm, the coelon, muscles, pharynx and salivary gland from certain 

 granular ectoderm cells, the circular muscles directly from the adja- 

 cent ectoderm and the excretory organs not from the entoderm but 

 probably from the ectoderm. A comparison is thus drawn between 

 the Rotifer and the Trochosphere — the great similarity being over- 

 balanced by the absence of mesoblasts. Thus the Rotifer is to be 

 regarded as an earlier stage than the Trochophore, wanting as yet 

 the special mesoderm mass. The Rotifer is thus not a sexually 

 mature Trochophere. Yet the possession of a subcesophageal ganglia 

 points out a resemblance to the Molluscan trochophore, while there 

 is also much resemblance to an ancestral form for the Polyzoa, Brach- 

 iopods and Chsetognaths. 



The " foot " of the Rotifer is not a ventral organ but to be regarded 

 as a tail or posterior end of the body, having at first a terminal anus 

 afterwards moved dorsally by the formation of a terminal adhesive 

 gland. The embryology of this region is accepted by the author as 

 homologous with that of the abdomen of Crustacea. 



While the Rotifers thus stand as representative.- of the ancestors^ 

 so many groups they themselves are to he divided, as the embryology 

 indicates, from the " I'rotroehophoni " of tin I'latvl.elniinthes. 



