( 87 ) 

 PEOGEESS OF MICEOSCOPICAL SCIENCE. 



Tlie American Hydrce. — A note has been read before the Society 

 of Natui'al Sciences of Pbiladelpliia by Professor Leidy on the two 

 species of Hydra common in the neighbourhood of Philadelphia. 

 One is of a light brownish hue and is found on the under side of 

 stones and on aquatic plants in the Delaware and Schuylkill rivers, 

 and in ditches communicating with the same. Preserved in an aqua- 

 rium, after some days the animals will often elongate the tentacula 

 for several inches in length. The gi-een Hydra is found in ponds and 

 springs, attached to aquatic plants. It has from six to eight tentacles, 

 which never elongate to the extent they do in the brown Hydra. In 

 winter this animal is frequently observed with the male organs de- 

 veloped just below the head as a mammal-like process on each side of 

 the body. He had not been able to satisfy himself that these Hydrce 

 were different from H. fusca and H. viridis of Europe. Professor 

 Agassiz had indicated similar coloured forms in Massachusetts and 

 Connecticut, under the names of H. carnea and H gracilis. Of the 

 former he remarks that it has very short tentacles, and if this is correct 

 under all circumstances, it must be different from om* brown Hydra, 

 which can elongate its arms for three inches or more. 



ItemarTcs on Actinojyhrys Sol. — Some observations made by Professor 

 Leidy at one of the recent meetings of the Society of Natural Sciences 

 of Philadelphia are not without interest. 



Professor Leidy, after describing the structure and habits of this 

 curious rhizopod, said that he had recently observed it in a condition 

 which he had not seen described. He had accidentally foimd two 

 individuals including between them a finely-granular rayless sphere 

 nearly as large as the animals themselves. These measured, indepen- 

 dently of the rays, "004 mm. in diameter; the included sphere 

 0'06 mm. He supposed that he had been so fortunate as to find 

 two individuals of Actinophrys in conjunction with the production of 

 an ovum. 



Preserving the animals for observation, on returning after an 

 absence of three houi's, the animals were observed connected by a 

 broad isthmus including the graniilar sphere reduced to half its 

 original diameter. Two hours later the granular sphere had melted 

 in the isthmus, leaving behind what appeared to be a large oil globule 

 and half-a-dozen smaller ones. The isthmus in the former time 

 measured -^^ mm., at the later time -^-g mm. Shortly afterwards, the 

 isthmus elongated and contracted to -^^ mm. on the left, while the 

 right half, retaining the oil globules, remained as thick as before. 

 At the same time the animals became flattened at the opp^isite poles. 

 The latter subsequently became depressed, so that the animals assiuned 

 a reniform outline. The isthmus, now more rapidly narrowed and 

 elongated, became a mere thread, and finally separated about one hour 

 from the last two hours indicated. The oil globules wore retained in 



