The Morphology of a Solenogastre. 723 
erinnert“, and the study of the post-larval stages of members of 
this group seems to show conclusively that the resemblance is more 
than superficial. Asis well known from the researches of KoWALEVSkI 
(1883) a mass of gland cells early appears in the chiton larva at 
the anterior border of the foot and in later embryonic life these 
open into a deep depression which in turn communicates with the 
exterior by numerous intercellular channels. This author made no 
study of the later stages of chiton development and consequently 
the complete history of this organ is wholly unknown. 
In looking up the subject in a series of embryos of Trachydermon 
raymondi, a fairly common species of chiton inhabiting the western 
shores of the United States, I have been able to determine the fate 
of this organ in a more definite way. Kowanzvskı looked upon 
this gland as a larval structure and in my study of the development 
of Ischnochiton (Heat, 1899) I considered this view correct and 
I have now no reason to modify my opinion for this organ grows 
but little after the metamorphosis of the larva and disappears at a 
comparatively early stage (within considerably less than a year). 
However it is of prime importance to note that before it vanishes 
it takes up a position beneath the buccal mass, still retaining its 
connection with the exterior for a long time. In the solenogastres 
it is a functional organ throughout life and not only occupies a 
position beneath the buccal mass but usually envelopes it to a 
considerable degree. Nevertheless except for the disparity of bulk 
a fundamental resemblance exists in both groups and I have no 
doubt whatever that they are homologous organs. 
While the anterior pedal gland sometimes opens into the ventral 
furrow without any direct connection with the foot there are several 
species in different genera where there is a longitudinal ridge which 
in Proneomenia hawaïensis appears to be merely the anterior end of 
the foot. It is not improable that this projection packed with 
ductules was not particularly serviceable in the movements of the 
animal and accordingly has come to be separated from the foot 
proper. 
The comparison of a set of organs as plastic as those composing 
the digestive system is, at the present time at least, of relatively 
small value. The general divisions, as the fore, mid and hind gut 
and such organs as the dorsal and ventral salivary glands, the 
stomach and liver doubtless have their recognized homolog in other 
classes of molluscs but a comparison of the finer details such as the 
