NATURAL SCIENCES OF PHILADELPHIA. 15 



yet continue to do so. While the highest forms of life may have 

 been slowly evolved from the simplest forms of the remotest age, 

 eqnalh' simple forms may have started into existence at all times 

 down "to the present period. From the later original forms new 

 ones may have been evolved to speed towards the same goal as 

 those which preceded them. 



February 10. 

 The President, Dr. Ruschenburger, in the chair. 

 Twenty-four members present. 

 The death of Prof. William Procter was announced. 



February 11. 



The President, Dr. Ruschenberger, in the chair. 



Twenty-six members present. 



On the Mode of Groioth of Desmids. Prof Leidy made some 

 remarks on the mode of reproduction and growth of the Desmids. 

 In illustration he described a common species of Docidium or 

 Pleurotseyiium. This consists of a long C3^1indroid cell constricted 

 at the middle and slightl}' expanded each side of the constriction. 

 When the plant is about to duplicate itself, the cell-wall divides 

 transversely at the constriction. From the open end of each half 

 cell there protrudes a colorless mass of protoplasm defined by the 

 primordial utricle. The protrusions of the half-cells adhere to- 

 gether and continue to grow. The bands of endochrome now ex- 

 tend into the protrusions and subsequently keep pace with their 

 growth. The protrusions continue to grow until they acquire the 

 length tyid form of the half-cells from which they started. The 

 exterior of the new half-cells thus produced hardens or becomes 

 a cell-wall like that of the parent half-cells. In this condition 

 two individuals of Docidium are frequently observed before sepa- 

 ration. During the growth of the new half-cells the circulation 

 of granules in the colorless protoplasm is quite active. In a 

 species of Docidium \\ mm. long by ^^ mm. broad, the growth of 

 the new half-cells was observed to be at the rate of about ^ mm. 

 In an hour. 



