JENNINGS: DEVELOPMENT OF ASPLANCHNA HERRICKII. 101 



other Rotifera. Cell lineage is traced to a much later stage than has 

 been done for other rotifers. 



3. In other respects the development of Asplanchna, so far as 

 observed, agi'ees in general with that of Callidina as described by 

 Zelinka ('91). The development of organs was not traced in Asplanchna, 

 the purpose of the work lying chiefly in the domain of cyto-mechanics. 



PART THIRD. - MATERIAL AND METHODS. 



The material for the studies here presented was collected by means of 

 towings from Lake Michigan and certain small lakes connected with it 

 in August and September of 1894. Such towings were killed and pre- 

 served by a variety of methods. For killing, the following reagents were 

 tried : (1) Flemming's stronger chrom-osmo-acetic mixture ; (2) Kleiu- 

 enberg's picro-sulphuric mixture, weaker solution ; (3) Henneguy's 

 fluid, consisting of Kleinenberg's weaker fluid plus 10% glacial acetic 

 acid ; (4) picro-nitric acid ; (5) alcoholic corrosive sublimate ; and (6) a 

 mixture of corrosive sublimate and formalin. The best results were 

 gained by the use of Flemming's mixture. The eggs were considerably 

 darkened, but this defect was easily corrected by bleaching with chlorine 

 generated from chlorate of potash and HCl. Henneguy's fluid and 

 picro-nitric acid also gave good results. By alcoholic corrosive subli- 

 mate the eggs were commonly shrunk, and with Kleinenberg's fluid the 

 shrinking was excessive. The towings after killing were preserved partly 

 in 80% alcohol, and partly in a mixture of equal parts of glycerine, 

 alcohol, and water. Both these preservatives gave satisfactory results. 



As is well known, the development of the embryo takes place in 

 Asplanchna within the body of the adult. The developing egg lies in 

 the posterior part of the body of the mother, enclosed in the greatly 

 distended oviduct or uterus, and with the ovary of the adult closely 

 applied to it. It was necessary to pick oat the Asplanchnas one by one 

 from the quantities of Crustacea and other plankton with which they 

 were mingled. This was done by using capillary tubes. It was necessary, 

 moreover, to assort them with respect to the state of development of the 

 contained embryo, if an embryo were present. This is a process involv- 

 ing great labor, as, in order to determine even approximately the stage 

 of development of the embryo, it is necessary to examine the animal 

 with the compound microscope. The majority of the specimens contain 

 an embryo; not rarely two are present, in difierent stages of development, 

 and in a single case I observed three. 



