1889.] Zoology. 643 
be distinguished, but they are usually not separate, and the hydrocoel 
remains opens to the anterior enterocoel. 
The crinoid Dipleunila develops only one anterior enterocoel, with 
which the hydrocal is at first connected, but afterwards becomes sepa- 
rate. There are two posterior enterocoels. In the Holothurioidea 
there is no right anterior enterocoel, and the left is rudimentary ; the 
hydrocoel, which is always on the left side, being connected with it. 
There are two posterior enterocoels. 
The last portion of the paper treats of the development of the skele- 
ton during this bilateral stage; it appears that many skeletal elements 
have their origin during this period. 
MoUusca. — Paul Pelseneer has contributed to the Archives de Bio- 
logic, a dissertation upon the morphological value of the arms of the 
cephalopoda, and arrives at conclusions which differ widely from those 
most generally received. The problem to be solved is whether the 
arms are of pedal or cephalic origin, — whether they are or are not essen- 
tially appendages of the head. He endeavors to answer this question 
by an examination of the nervous system, which he illustrates in two 
plates. From this examination he deduces that the comparative ana- 
tomy of the nerves is contrary to the cerebral origin of the brachial 
ganglia, and in favor of their pedal nature. From a comparison of a 
walking gastropod with a walking cephalopod, it is evident that the 
arms of the latter stand in precisely the same relation to its head as 
does the foot of the former to its head. The only difference is that in 
the cephalopod adult some of the arms have assumed a position in 
advance of the mouth. But in the cephalopod embryo the mouth 
opens dorsally as in the gastropod, and is in advance of the 
arms. The entire vitelline sac was, according to Pelseneer, taken 
for the foot by Balfour and by Brooks, but the margins of the foot per- 
sist around this vitelline sac, and the arms represent the margins of 
almost all the foot. The swimming-lobes of Pteropoda and the Aply- 
siidae correspond to the lateral borders of the foot in the gastroix)d, 
and may thus be compared with the arms of the Cephalopoda. Thus 
these arms are not merely the propodium, but represent the margin of 
almost the whole gastropod foot. The siphon (entonnoir) is the epi- 
C. R. Keyes gives an annotated catalogue of the MoUusca of Iowa, 
in the Bulletin of the Essex Institute, Vol. XX., in whi^h he e 
151 species now existing, and thirty-two from the loess of the s 
