VI 



Thus modified, the series corresponding with that entitled in the 

 synopsis, ' Incubation of the ovum in birds/ now exhibits all 

 the successive stages described by Mr. Hunter in his admirable 

 account of the ' Progress and peculiarities of the chick*.' 



It seemed a sufficient reason for suppressing the twenty-first 

 series of the ' Synopsis/ that the preparations included therein 

 exhibited stages of development nearly connected with those 

 which preceding series were expressly established to demonstrate. 

 The preparations illustrative of generation by artificial fission f 

 have thus been re-united to those exhibiting the same effects by 

 spontaneous fission f. The preparations exhibiting the ' changes 

 of the tadpole into the frog ' are now combined with the 

 analogous and connected specimens constituting the group en- 

 titled { Ova of animals which have gills when hatched, but 

 afterwards lungs ||.' By thus combining the later with the 

 earlier stages of development in the oviparous classes, the con- 

 secutive phenomena of such development in one series are 

 brought under the immediate observation of the physiological 

 student, and he is made familiar with the earlier stages of the 

 formation of the vitellicle and allantois before he arrives at that 

 series (the nineteenth in the synopsis) in which further changes 

 of the allantois are exhibited, and its subserviency to the forma- 

 ation of the placenta is demonstrated. 



The preceding observations explain the plan of arrangement 

 adopted in the present catalogue of the Hunterian physiological 

 collection. The following remarks refer to the descriptive part 

 of the same catalogue, and particularize the sources of the 

 additional information that may be found in the present, when 

 compared with the previously existing catalogues. 



The printed synopsis, already quoted, is limited to an expla- 

 nation of the subjects of the several series and subseries of 

 specimens. The catalogues descriptive of the individual speci- 

 mens have hitherto existed only in manuscript. 



* Introd. to the Fifth Volume, p. viii. 



t Series XXI., Subseries 219. J Series XVII., Subseries 170. 



Series XXI., Subseries 222. || Series XVIII., Subseries 194. 



