138 THE ROTIFERA. 



Tho conclusion socms a lamo 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 Auat. of Kot. aurita ; " Tr. Micr. Soc. 

 Lond., iii. 98),— that the vascular system is a proper respiratory system, and that the 

 lateral canals are proper branchia;. The water enters at the head, circulates, and is 

 poured out at tlie 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 ; " 

 (3) the vibratile tags ; (4) the contractile vesicle. 



1. In so many species that I consider the arrangement universal, I trace up tho 

 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 Fterodina, (especially in patina and clypeata) the tubules ramify and 

 spread into broad fan-shaped plexuses of flat laminre (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 cesophagus 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 Ptcrodina makes this doubtful ; and a number of other curious facts are 

 observable, which confirm, more or less manifesily, this connection. 



Sometimes these organs take the form of large reservoirs of delicate texture and 

 wrinkled surface, joined to the cesophagus 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 OBSophagus, 

 while the canal seems in some inexplicable way miited with both. This, excessively 

 slender at its origin, expands as it proceeds, becoming corrugate, till it attains a width 

 almost rivalling the plexus of Ptcrodina 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 Notholca acuminata the "gastric gland" much resembles the ;j?/r//br?7i of Pter. 

 valvata, with a slender duct to the long oesophagus, and another duct from an outer 

 an"le 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 Una has a structure somewhat like this ; and, in a less degree, Metopidia 

 rlwmboides. 



Several species of Brachionus display anomalies in these organs. Thus in B. BaJccri 

 and B. urceolaris each is a great wrhikled sac of very delicate tissue, and of retort-shape, 

 at the end of a long neck. In B. riihens there are tico sacs on each side, united by a 

 long sinuous duct. In B. Milllcri 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 



