PLATE XIII. 



Fig. l. Micrura alaskensis. Transverse section through mouth region. The 

 peculiar accessory buccal glands (bg') are seen to lie outside the cir- 

 cular muscular layer (cm), and amongst the fibers of the outer longi- 

 tudinal muscular layer (olm). Their secretion passes through the layer of 

 circular muscles, and mixes with that of the true buccal glands (bg), 

 which lie immediately beneath the epithelium of the mouth ( mep). The 

 buccal nerves (bn) lie on the lateral borders of the mouth as usual. 

 Other reference letters are explained on p. S3. (X 3). 



2. Zygonemertes thalassina. Transverse* section immediately back of the 

 brain. The intestinal caeca (ic) reach forward to abut against the dor- 

 sal ganglia. The ocelli (oc) extend back of the brain, and occupy posi- 

 tions, as shown, immediately above and external to the lateral nerve 

 cords (In). (X 100). 



3. Amphiporus angulatus. Transverse section through posterior end of 

 body. The drawing is slightly diagrammatic, as it contains portions of 

 the two adjacent sections. The anastomosis of the three longitudinal 

 blood vessels (bva) is seen to lie immediately dorsal to the commissure 

 ( nc) of the lateral nerves (In) ; the basement layer (bm) is remarkably 

 thick in this region. The posterior end of the intestine (in) opens 

 ventrally a few sections farther back. Other reference letters are ex- 

 plained above. (XSo). 



(no) 



