MUSEUM OF COMPARATIVE ZOOLOGY. 61 
and Crisia. The existence of two layers was easily demonstrated in all 
cases in the young polypide by cross sections of the “neck.” The two 
layers are of nearly the same thickness, and distinctly separated from 
each other. The presence of two layers in the adult is more difficult to 
determine, but it was always indicated by the occasional presence of 
two nuclei lying side by side, and especially at the attachment to the 
diaphragm. The presence of muscles was demonstrated in all cases 
(except Bowerbankia, where my few sections did not show the proper 
region) upon tangential sections of the sheath, I may add, that the 
existence of muscles is wellnigh conclusive @ priort evidence of the 
existence of the mesodermal layer, since nowhere else in Bryozoa, so far 
as I know, do muscles arise from any other layer. Prouho’s evidence in 
support of his position is perfectly satisfactory to my mind, certainly 
more so than the negative evidence of Seeliger in support of able hi 
further support of my statements I may refer to the condition of the 
kamptoderm (kmp’drm.) in Figures 92 and 83, Plate X. 
Nervous System. — Since Dumortier discovered, in 1835, a ganglion in 
Lophopus, there has been seen in marine as well as fresh water Bryozoa 
a body which has been considered, with greater or less certainty, to con- 
stitute the central nervous system. Overlooked by Farre, it was, I be- 
lieve, first described for marine Gymnolemata in 1845 by van Beneden, 
co-worker with Dumortier, for Laguneula (Farrella). Nevertheless, up 
to the present the evidence of its being a ganglion homologous with that 
of Phylactolamata has not been satisfactory. The homology can be estab- 
lished only by determining its similar origin with the brain of Phylacto- 
lemata ; its function can be best established by showing the existence of 
ganglionic cells and fibres. I hope to have advanced our knowledge in 
both of these directions. 
At about the time that the œsophagus and stomach have become con- 
fluent, one notices a papilla-like elevation of the floor of the atrio-pha- 
ryngeal cavity. This has been noticed by Korotneff (74) in Paludicella, 
and by Nitsche (71, p. 459) and Seeliger (’90, p. 586) in Cheilostomes, 
It has been called by them “ Epistome,” and compared with that of Endo- 
procta or Phylactolemata. In my own opinion, it is merely a structure 
brought into prominence by the sinking down of the floor behind it to 
form the ganglion (Plate X. Fig. 86, gn.). This depression has been 
scen by Barrois (’86, pp. 74, 75) and Prouho C90, p. 450), and rightly 
interpreted by them as probably destined to give rise to the central 
nervous system. That this is the correct interpretation is shown by 
later stages from different species, as Figures 89 and 83, in which we see 
