Here is what is happening in the chrysalis. Inside the chrysalis, the caterpillar is becoming completely liquid (soupy) and reforming itself into a butterfly. The butterfly pushes from inside and slowly struggles out, until the case splits open.
A cremaster is a support hook (or a cluster of small hooks) at the abdominal (hind) end of a pupa. Some butterflies (like the Monarch butterfly) are supported by only the cremaster; others, like this Eastern Black Swallowtail attach to the support with the cremaster and bands of silk (called the girdle) around the mid-section.
The caterpillar's skin is shed for the last time as it passes from the larval (caterpillar) stage to the pupa (chrysalis) stage of metamorphosis. Under the caterpillar's skin this time is a jade green casing which is called a chrysalis. Inside the chrysalis, which is only about an inch long, the caterpillar will miraculously transform into a beautiful butterfly.
|The pupa is the stage in a butterfly's (or moth's) life when it is encased in a chrysalis and undergoing metamorphosis. Wings develop during this stage.|
About a day before the adult butterfly emerges, the chrysalis becomes transparent.
Here is a 200X look at the "air vents". Next post I will tell you what happened next!