138 THE ROTIFERA. 
The conclusion seems a lame one, and yet I fear that it is hardly possible to hope for 
a better, when dealing with an apparatus of whose structure we know so little ; one which 
we are unable to examine except with our eyes, and yet one in which we have strong 
reasons for suspecting that, on crucial matters of detail, our sight deceives us. 
P.H.G. on the Vascular System. 
[My opinion is,—as it was in 1850 (‘‘On the Anat. of Not. awrita;”’ Tr. Mier. Soe. 
Lond., iii. 98),—that the vascular system is a proper respiratory system, and that the 
lateral canals are proper branchie. The water enters at the head, circulates, and is 
poured out at the cloaca. I believe these three facts may be predicated of the entire 
class. Accessories to the process are: (1) the afferent tubules ; (2) the ‘gastric glands ;”” 
(83) the vibratile tags ; (4) the contractile vesicle. 
1. In so many species that I consider the arrangement universal, I trace up the 
canals to the funnel through which the head-mass constantly moves up and down. The 
canals never partake of this motion, and it is evident that they are attached to the wall 
of the funnel, which I presume to be perforated with minute orifices through which the 
external water constantly percolates into the afferent tubules. In many species these 
appear to be numerous, and they are seen to branch and to anastomose very irregularly 
into each other, forming single, double, or multiple canals, which run, sometimes nearly 
straight, but more commonly bent sinuately in various degrees, throughout the length of 
the animal. In Pterodina, (especially in patina and clypeata) the tubules ramify and 
spread into broad fan-shaped plexuses of flat laminze (which I consider tubular, and ciliate 
within), filling the wide triangular areas on each side of the mastax. Then they begin 
to unite again, and presently (in P. valvata especially), bending abruptly from the ven- 
tral to the dorsal side, form one broad and long pyriform sac which narrows to a long 
slender duct, and joins the esophagus one on each side, pouring the effete water into the 
alimentary canal, and ultimately through the cloaca, without the intervention of a con- 
tractile vesicle. 
2. The ‘“ gastric glands.”—The organs thus named have usually been considered as 
ancillary to the digestive system. But their evident connection with the aquiferous 
system in Pterodina makes this doubtful; and a number of other curious facts are 
observable, which confirm, more or less manifestly, this connection. 
Sometimes these organs take the form of large reservoirs of delicate texture and 
wrinkled surface, joined to the esophagus by long ducts, and affixed by threads (perhaps 
tubular) to the lateral canals, or to the lorica. In Metopidia solidus, each appears as 
an aggregation of saccules into a large three-sided and three-angled body, one angle 
passing up to the origin of the canal, and another by a long duct to the cesophagus, 
while the canal seems in some inexplicable way united with both. This, excessively 
slender at its origin, expands as it proceeds, becoming corrugate, till it attains a width 
almost rivalling the plexus of Pterodina patina, just before it enters the cloaca, without 
the intervention of a contractile vesicle. Yet, in some individuals, the contractile 
vesicle itself and its action are quite distinct. 
In Notholea acuminata the ‘ gastric gland”? much resembles the pyriform of Pter. 
valvata, with a slender duct to the long csophagus, and another duct from an outer 
angle leading down for some distance closely parallel with the lateral canal, and con- 
nected with it by a short transverse duct at each end. 
Cathypna luna has a structure somewhat like this; and, in a less degree, Metopidia 
rhomboides. 
Several species of Brachionus display anomalies in these organs. Thus in B. Bakert 
aud B. urceolaris each is a great wrinkled sae of very delicate tissue, and of retort-shape, 
at the end of along neck. In B. rubens there are two sacs on each side, united by a 
long sinuous duct. In B. Miilleri there is but one on each side, but it is cleft almost to 
the base into two varying portions. In all these the organs seem to have more or 
