ORTMANN: A MONOGRAPH OF THE NAJADES OF PENNSYLVANIA 305 
certain other structures (flaps and papille of the edge of the mantle), which most 
emphatically serve for the aération of the marsupium, and thus are to be regarded 
as adaptations to a long breeding season. 
Having thus correlated physiological function with anatomical and morpho- 
logical structures, we may rest assured, that we have discovered an essential prin- 
ciple in the development of the Najades, and we may say with all confidence that 
a systematic arrangement, which is founded upon such structures, which we are 
able to understand, must be the correct one. Sterki’s discovery of summer- and 
winter-breeders, although originally not fully understood, thus becomes the most 
important step in our knowledge of the system of the Najades. 
4. The discharge of the Glochidia. 
As may be inferred from the above, the discharging of the glochidia must 
take place at two different seasons: in the bradytictic forms in spring or early 
summer (April to June), in the tachytictiec forms from the end of June to August. 
While this fact is beyond doubt, the manner of discharge remains yet to be in- 
vestigated, and for some time this proved a serious puzzle to me. But now I 
am satisfied that my observations are complete enough to answer the question. 
Lea repeatedly observed the discharge of the glochidia and placente, but he 
only mentions that they come out of the shell at the posterior end (in Lampsilis 
radiata, L. parva, Strophitus edentulus (Observ. X), and Unio complanatus (Observ. 
II), and he further quotes (Observ. III) a similar fact as observed by Kirtland in 
‘Quadrula cylindrica. As we shall see, these observations are probably correct, 
and represent the normal conditions. 
On the other hand, Lea (Observ. II, p. 52) reports that in a gravid female of 
Anodonta fluviatilis (= cataracta) he made the young come “from the orifice at 
the inferior part’’ (= edge) of the marsupium, by the pressure of his fingers upon 
the sides of the marsupium. I consider this not normal, but an artificial effect, 
in fact, there are no such “‘rifices.”’ 
Other authors do not treat of the discharge of the glochidia, except that 
Simpson (1900, p. 616) incidentally expresses the opinion, that in Strophitus the 
placentule are discharged through the walls of the gills, which, as I believe, is 
entirely wrong. 
Sometimes it is postponed to the beginning of July, chiefly so in Lake Erie. Lea has repeatedly and in various 
species observed discharges during winter. These always took place, however, in the case of specimens kept in captivity 
under artificial conditions, which probably induced an abnormally early discharge. Since the glochidia of bradytiectie forms 
are fully developed in the beginning of the winter, artificial conditions (temperature for instance) might start the discharge 
at any time during the winter. 
