NATURAL SCIENCES OF PHILADELPHIA. 41 



stance. Their reproduction is exceedingly simple, being a splitting 

 of their body into halves, each half developing into a new Monas. 



The absence of a nucleus characterizes the chief point of distinc- 

 tion between these and the Amoebse. A Sponge may be con- 

 sidered as a colony of Amcebse; the individual members of which 

 are united by a common bond of union ; this view is suggested 

 by the young of the Sponges, which cannot be distinguished from 

 Amcebee. The development of flagella and cilia, as in Euglena, has 

 led the way to the Animalcula or Infusoria. Nor need we confine 

 our attention to these simple forms of animal life. 



As we ascend the scale, we meet with equally forcible illustra- 

 tions. Prof. Cope, in his " Origin of Genera," in writing about 

 the higher Cervidse, affirms that " Rusa and Axis never assume 

 characters be} r ond an equivalent of the fourth year of Cervus. In 

 Dama the characters are, on the other hand, assumed more rapidly 

 than in Cervus, its third year corresponding to the fourth of the 

 latter, and the development in after years of a broad plate of bone 

 with points being substituted for the addition of the corresponding 

 snags, thus commencing another series." 



In the Cephalopoda a number of series of remarkable regularity 

 can be established. The advance in the first place being in the 

 complicated arrangement of the plicae of the external borders of 

 the septa ; in the second place, in the approach which one or both 

 extremities of the shell make to the spiral ; and, lastly, in the posi- 

 tion of the siphon. Alpheus H} r att, in an interesting and import- 

 ant essay upon this topic, makes the assertion that the less complex 

 forms are identical with the undeveloped condition of the more 

 complex. His language is, "There is a direct connection between 

 the position of a shell in the completed cycle of the life of this 

 order, and its own development. These shells occupying the 

 extremes of the cycle, the polar forms, being more embryonic than 

 the intermediate forms." 



Such evidence as has just been adduced of the gradual modifi- 

 cation of living species, some of the separate links of the chain 

 which bind the less with the more highly specialized, being ob- 

 servable in the history of development of individual species, is of 

 the most positive and satisfactory character. Can we bring for- 

 ward similar evidence in confirmation of the position that the 

 Sphinges are directly descended from the Tineidsf I apprehend 

 not. Whence the simultaneous occurrence of these two forms in 

 4 



