No. 401.] DEVELOPMENT OF PENNARIA TIARELLA. 395 
entrance of the sperm produces a profound effect upon the 
egg, which up to that time has been quite passive. Examined 
under a low power the egg very soon after access of the sperm 
shows a sort of convulsive surface torsion, which after a few 
minutes quite disappears, and the egg again becomes quiescent. 
But within half an hour, often sooner, the phenomena of cleav- 
age begin and usually go forward with comparative rapidity, 
the entire process, so far as surface features are concerned, 
becoming complete within a few houts, though varying greatly 
in different eggs and under slight differences of temperature. 
V. CLEAVAGE. 
Of cleavage phenomena in Pennaria it is extremely difficult 
to formulate an account, and that for several reasons. A glance 
at the figures which present only some of the more striking 
aspects of the subject will afford one, and perhaps a sufficient, 
reason. Again, the unusual opacity of the eggs renders diffi- 
cult, either in the living or preserved material, any critical 
insight into other than the surface phenomena. There seems 
to be no law or order attending the process. Every egg isa 
law unto itself and is absolutely indeterminate as to order or 
rate of development. Beyond the accounts of Wilson for Ren- 
illa (84), and Metschnikoff for Ratkea and Oceania (86), the 
literature at my command affords nothing comparable, and 
these are only remotely so. Andrews (98) points out * Some 
Ectosarcal Phenomena in the Eggs of Hydra," which, while in 
some features they are similar to some aspects associated with 
these phenomena in Pennaria, seem yet to be of a decidedly 
different character. Similar ectosarcal features were more or 
less obvious in the eggs of Pennaria, bits of protoplasmic mat- 
ter at times being extruded and even detached from the sur- 
face of the egg, including at times considerable portions. 
Again, the presence of more or less definite protoplasmic bands, 
or bridges, during the earlier phases of cleavage is a very con- 
Spicuous feature in Pennaria. That it may in some way be 
associated with fertilization, the entrance of several Spermato- 
zoa, artificial conditions, or otherwise, would seem not improb- 
