[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
from what I have been able to make out of the vegetation in the
topmost cretceous layer in Alberta (the top 2 meters of strata)
angiosperms were confined to stream-sides. The general flora
was savannah-like (but no grasses) with low-lying sward of
small ferns and occasional scattered trees. No dense forest.
That c ame in only i mmediately after the K-T boundary, when
a coal layer, immediately overlying the boundary gives signs
of a dense forest. Perhaps with no large h erbivores to
graze it all down the trees had a chance to survive?
Multiple matings by birds.
Unlike mammals (the ones that have large litters) female
birds do not produce all their eggs at one time, but over
a prlonged period, often with gaps o f o ne or two days
between successive eggs. Thus if a female mates several
times successive eggs could be fertilized by di fferent males.
The sperm from several males could be mixed inside the
receptaculum seminis (a sac where the female stores sperm
until it is needed) so competition at the sperm level is
Different zoologists use the work "penis" in different ways.
To some it means any i ntromittent organ or ograns. Others
define it to mean any inromittent organ that is divorced
from the alimentary system. That would mean that the
only true vertebrate penis is the mammalian one, but many
invertebrates have intromittent organs that have nothing
to do with the gut. Insects and crustaceans for i nstance.
The i nsect i ntromittent organ is generally called a penis
by entomologists, and details of its anatomy are often used
to diagnose species. In decapod Crsutacea the intromittent
organs are paired structures formed from the the fi rst pair
of abdominal swimming legs.
Others define a penis as a si ngle central intromittent organ.
Under this definition the penis of an isect is a true penis,
even though it has no phylogenetic relationship to the penis
Others define penis as being any central organ, not derived
from or associated with the alimentary system, that is tubular
for co nduction of sperm. Lots of invertbrates have organs
of this kind.
Another definition regards a penis as a single central
organ. This excludes the lizard and snake condition of
hemipenes, but i ncludes a few birds, like ducks.
You can take your choice, but don't define "penis"
simply i n terms of what occurs in vertebrates. Consider
inverts too. For myself I generally use penis to mean
any intromittent organ, since it is shorter, and in
context is not likely to be confusing.
>From: David Brez Carlisle