920 REPORT—1850. 
ceeded in detecting anything like a complete collar surrounding the tube at 
this place. There is no other ganglion than the one just deseribed, and 
nothing which can with any real probability be referred to an organ of 
special sense has as yet presented itself. 
To M. Dumortier is due the credit of having first demonstrated the exist- 
ence of a nervous system in the Polyzoa. He saw in Lophopus erystallinus* 
the subcesophagean ganglion, though he speaks doubtingly of it as referable 
to the nervous system, while he assures us of a distinct ganglion placed at 
the base of each arm of the lophophore. This last is certainly an erroneous 
observation, and it is probable that the learned Belgian naturalist mistook 
for a ganglion the optical expression of the cavity of the arm when seen in 
transverse section. 
11. Organs for the Preservation of the Species.—Embryology. 
In the Polyzoa, both marine and freshwater, three distinct modes of re- 
production may be witnessed, namely, by buds or gemme, by true ova, and 
by free, locomotive embryos. 
1. Reproduction by Gemme.—The gemme always originate in the endo- 
eyst. In Lophopus, Alcyonella, Flumatella and Fredericella, they occur with- 
out any very regular order near the mouth of the cell. They at first appear 
‘as a small tubercle projecting into the perigastric space, but may soon be 
seen to take a development in an outward direction. The bud now presents 
the appearance of a vesicle projecting from the exterior of the parent cell, 
closed: at its external or free extremity, but having its cavity in communica- 
tion with the perigastric space. The polypide is gradually developed in the 
interior of the gemma, which soon opens at its free extremity so as to admit 
of the exsertion and retraction of the young polypide. ‘The gemma is now 
a complete cell with its contained polypide, and in the branched species soon 
grows into a new branch springing from the side of the old one. In Crista- 
tella the gemme are produced very regularly from the external side of the 
last-formed series of cells, and constitute a marginal series extending round 
the entire cclony. Finally, in Paludicella the gemme are also exceedingly 
regular, always originating at a fixed point a little below and at each side of 
the orifice. From this position of the gemmz, two opposite branches spring 
from the thick end of each cell; and though these branches are by no means 
necessarily developed on every cell, yet the fixed points on which they ori- 
ginate, and the constant angle at which they are given off from the parent 
cell, give to the whole colony a very regular and elegant appearance. 
It is difficult, on account of the nature of the intervening structures, to 
follow the process of development of the polypide in the gemmz of any of 
the species with the exception of Paludicella ; in this, however, I have been 
able to trace its gradual formation from a very early stage to its complete 
development. 
The gemma in the earliest condition in which I have been able to observe 
it, appears here as a minute tubercle projecting from the external walls of 
the cell, and filled with a granular parenchyma. We next find it hollowed 
out into a cavity which communicates with the interior of the parent cell. 
The tubercle with its cavity increase in size, and the gemma is now found 
to consist of an external envelope continuous with the ectocyst of the parent 
cell, and of a thick fleshy lining continuous with the endocyst; this internal 
tunic has numerous large round nucleated cells distributed through its sub- 
* Dumortier, loc. cit. 
