A New Rotifer, Lacinularia striolata. 23 



colony. These fixed colonies were amenable to the paraffin 

 method of obtaining serial sections. The stain most successful 

 of those tried was picro-carmine. Considerable care was necessary 

 to pass the specimens through increasing strengths of alcohol and 

 to clear with oil of cloves. A colony thus placed in serial 

 sections of course gave sections through individuals in every 

 possible plane. The results obtained show that a combination 

 of tlie section method with the older plan of examining the 

 living animal is preferable to following either system exclusively. 

 Digestive System. — The trochus (Fig. 3, t.) and cingulum 

 (Fig. 3, c.) form separate and complete circuits, and the groove 

 between them is continuous round the disc. The cingulum runs 

 backwards ventrally, forming a triangular space in which is 

 placed the mouth (Fig. 3, m.). The mouth is slit-like, but wider 

 at the anterior, and opens into the buccal cavity (Fig. 5, b.c). 

 This has a thin roof, and sections parallel with the plane of the 

 disc show a triangular outline widest remote from the mouth, 

 and downwards the walls rapidly converge and form a short 

 funnel terminating in a very narrow pharynx. Nearly the 

 whole of the buccal cavity is thickly covered with cilia. The 

 pharynx (Figs. 5, 6, 7, p.) is close to the ventral surface. At 

 its commencement there are two small openings (Figs. 6 and 7, 

 s.d.) into it, one on either side, which I take to be ducts for the 

 passage of the salivary secretion from two nucleated cells (Figs. 

 6, 7, 8, s.g.) situated on the floor of the buccal cavity, one on 

 either side of the pharynx. These cells have definite borders, 

 are spongy looking, stain faintly, and do not occupy the whole 

 of the space surrounded by the outer wall, as there appears an 

 unoccupied portion at the base of each. The pharynx is short, 

 and at its lower part becomes a flattened cavity curving round 

 the food cavity of the mastax, extending dorsally a short distance, 

 and ventrally and posteriorly close under the cuticle of the 

 ventral surface, where it terminates about the level of the trophi 

 (see Fig. 5, p. and tr.. Fig. 7, p.). This flattened portion com- 

 municates with the food cavity by a slit extending along its 

 length (Fig. 7, si., the T-shaped opening shows the part curved 

 backwards cut across). The cilia on either side shown in Fig. 7 

 are from the inside of the food cavity, being cut off" by the 

 section knife. This slit will serve as a valve to regulate the 



