52 DR J. H. ASHWORTH 



posterior margin. The skeletal substance of the lophophore is therefore approxi- 

 mately U-shaped. This substance is, in these specimens, almost homogeneous and 

 contains neither cells nor nuclei ; it has evidently been secreted by one or both of the 

 cell-layers in contact with it. 



The mouth-cavity and oesophagus are lined with ciliated columnar cells, and 

 the anterior and posterior walls of the stomach with high and narrow flagellated 

 cells, those of the posterior portion of the stomach being especially striking. The 

 intestine is apparently not ciliated. The digestive glands or " liver "-lobes are thick- 

 walled diverticula of the mid-out. There are two anterior dorsal diverticula — the 

 smallest and last formed "liver "-lobes — situated in the dorsal and anterior part of 

 the body-cavity ; they are bounded laterally by the occlusors, and extend backwards 

 as far as the gastro-parietal bands and forwards to the level of the anterior edge of 

 the occlusors (fig. 8). These lobes unite ventrally and open into the anterior dorsal 

 wall of the stomach by a very short median duct ; dorsally the lobes are separated 

 by the dorsal mesentery. The large posterior dorsal lobes of the digestive gland — 

 one right and one left — open separately into the dorso-lateral portion of the stomach 

 about the middle of its length (fig. 9). Each of these lobes presents an indication 

 of subdivision into anterior and posterior portions. The ventral lobe of the "liver" 

 is a large, A-shaped diverticulum (fig. 10) — that is, it is subdivided into right and 

 left portions, which open by a common aperture at their anterior ends into the 

 stomach near the middle of its ventral wall. The cells composing the "liver" are 

 highly vacuolated — the vacuoles contained in life digestive secretion and oil globules, 

 — cell-outlines are not distinguishable, and the nuclei are comparatively small. 

 When the contents of the vacuoles have been removed, the walls of the " liver "- 

 lobes have a spongy appearance, and embedded in them, here and there, are the 

 unicellular algse * on which the larva principally feeds. 



The two ccelomoducts (nephridia) could be clearly seen in the living larvae, and 

 are well. seen in some of the whole mounts and in the sections (fig. 10). Their 

 funnels, the apertures of which are directed postero-medially, lie in the ccelom near 

 the posterior end of the mid-gut, and are on the ileo-parietal bands. Each ccelomo- 

 duct, the lumen of which is narrow, runs forwards in a curved course, and opens into the 

 mantle-chamber on the antero-ventral wall of the body proper, immediately lateral to 

 the anterior occlusor muscle — that is, ventral and a little postero-lateral to the mouth. 



(v) Larvae with 14 or 15 pairs of cirri. — Four large specimens were found in 

 the Red Sea, two of them on June 21 at locality (i), the others on October 22 at 

 locality (iii). The measurements of their shell-valves are — 







Length. 



Breadth. 



", 



October 22, 1914 



1-47 mm. 



1'22 mm. 



K 



June 21, 1914 . 



. 1-48 „ 



1-22 „ 



c, 



October 22, 1914 



• 1-52 „ 



1'22 „ 



d, 



June 21, 1914 . 



• 1-6 „ 



1-37 „ 



* A Radiolarian was also noticed in the gut. 



