JENNINGS: DEVELOPMENT OF ASPLANCHNA HERRICKIL 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, agrees 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-mechanies. 
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-acetio mixture; (2) Klein- 
enberg’s piero-sulphurio mixture, weaker solution; (3) Henneguy’s 
fluid, consisting of Kleinenberg's weaker fluid plus 10% glacial acetic 
acid; (4) piero-nitrie 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 HCI. Henneguy’s fluid and 
picro-nitric acid also gave good results. By alcoholic corrosive subli- 
mate the eges 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, enelosed in the greatly 
distended oviduet or uterus, and with the ovary of the adult closely 
applied to it. It was necessary to pick out 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 involy- 
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 different stages of development, 
and in a single case I observed three. 
