286 



exceedingly valuable to have so cultivated a thinker as the 

 author treating morphology apart from this power, for so far 

 he here stands almost alone as the representative of unbiassed 

 thought. 



There are two points in which we may venture to express 

 dissent from the author's classificatory views, and there 

 are probably many others in the book which are open to dis- 

 cussion, but make their enunciation by Professor Kolleston 

 none the less valuable and interesting. Above we have 

 quoted a sentence in which Dr. Rolleston says he would 

 assign a rank to Spongiadae among the Protozoa equal to 

 that held by E-hizopoda, and for the same reason, viz., the 

 polymorphism exhibited by some of the forms of these groups. 

 We cannot call to mind any polymorphism in the E.adiolaria 

 to which Dr. Rolleston alludes, for simple aggregation does not 

 constitute polymorphism, and the association of units to form a 

 secondary aggregate is carried no further in these creatures. 

 In the sponges, on the other hand, there is most complete 

 polymorphism amongst the primary units, that is to say, 

 " histological differentiation " ; and not only that, but the 

 secondary aggregates formed of these differentiated elements 

 with cndoderm and ectoderm, antimera, and central osculum, 

 exhibit polymorphism in their aggregation to form tertiary 

 aggregates in some cases, so that certain abortive " persons," 

 as Haeckel terms them, share the mouth of a central " person." 

 These characters of the sponges seem to us to separate them 

 by a huge gap from Rhizopoda, among which we never see a 

 trace of " division of labour " structurally expressed, or indi- 

 viduation, in connection with the aggregation of units in such 

 forms as are compound, and they go far to justify Haeckel's and 

 Leuckart's placing of Spongiadoe as Coelenterata. Our second 

 point is as to the dissociation of Trematods and Leeches, and 

 the arrangement of the latter with the Chaetopods. We are 

 strongly persuaded that the digestive, vascular, reproduc- 

 tive, muscular, tegumentary, and locomotive system of 

 the Leeches are but slight modifications of the Trematod^s, 

 and suspect that in placing Discophora with Cha?topods, 

 too much weight is given to a physiological phenomenon 

 of great variability, viz., the presence of the PlGemoglobin 

 in the vascular fluids (not in homologous vessels) of the 

 two groups of worms, which have but very remote genetic 

 affinities. 



To the private student, and indeed to many teachers, a 

 more exact account of methods of and apparatus for dissection 

 in different cases would have been very valuable, and we feel 



