cial sections) of a single polyp into several distinct com- 

 plete bodies. The sexual fructification takes place only 

 in the months of September and October, as is the case 

 with many Crustaceans (Daphnia, Sid a, etc.) The 

 Hydra vulgaris produces no hydro-medusarium, as al- 

 most all Hydroid -polyps do. (L. Agassiz). 



Of the worm type, (he species Nais Probosctdea pre- 

 dominates, (plate II, fig. VI, with natural length of 1, 

 to 2,0 Mm.) which is very thin, with a still thinner pro- 

 boscis. They reproduce very rapidly, by sexual fructi- 

 fication and by separation into parts, every fragment be- 

 coming a perfect animal, and the division may be con- 

 tinued indefinitely. 



This phenomenon is caused partly by the multiplying 

 of the body -cells and partly by the division of the body- 

 segments (the so-called gemmipar and fissipar multipli- 

 cation, (Carl Gegenbaur). The process begins always 

 with the division of one metamere into several, which 

 together form a complete, new individual. 



In ^sTais Proboscidea the advance in cellular differentia- 

 tion of several segments was noted by me in specimens 

 found in a little pond in the Central Park. TheJNais are 

 found mostly in the sediment of the Croton water ; their 

 movements are wavy, snake-like. 



The Bryozoans are found as greyish-white, branched 

 pieces of a leathery consistence in the sediment of the 

 water. The representative species being Plumatella Re_ 

 pens (plate II, at the figure IX, n), and Cristadella 

 Mucedo. Viewed by a 70 to 100 diam. magnifying power, 

 they offer to the eye a magnificent view by the movements 

 of their tentacles (feelers), their manner of securing 

 food, and other curious habits. They may be found in 

 the summer-time in any of the small ponds of the Cen_ 

 tral Park on almost every stone, which they cover with 

 their body-tubes (integumentum) like a moss. I saw the 



