REPORT ON THE NEMERTEA. 



41 



brain-lobes do not open out in the lower angle of the fissure but far forwards, in agree- 

 ment with the situation of those lobes. 



It will perhaps best serve the purpose of conveying an idea of the relative situation 

 of the more important organs in the head and trunk to give, as was done for the fore- 

 going species, the number of the section of the whole transverse series (into which head 

 and anterior oesophageal region were cut up) in which these organs occur. 



We then find: — 



Section 30. First appearance of the lateral blood- 

 lacunae in the head. 



Sections 64-66. Superior commissure of the brain- 

 lobes. 



Sections 71-78. Inferior commissure of the brain- 

 lobes. 



Section 80. Left canal from cephalic fissure into 

 posterior brain-lobe. 



Section 87. Right canal from cephalic fissure into 

 posterior brain-lobe. 



Sections 84-104. Left posterior brain-lobe. 



Sections 89-105. Right posterior brain-lobe. 



Section 71. The median blood-vessel enters the 

 proboscidian sheath. 



Sections 350-360. It again leaves it. 



Sections 129-159. Mouth. 



Section 129. First appearance of the nephridial 

 canals just above the level of the longitudinal 

 nerve-trunk. 



Sections 355-400. Left deferent ducts of nephri- 

 dial system. 



Sections 329-335. 

 dial system. 



Right deferent ducts of nephri- 



These two deferent ducts (the only pair) are seen in the same section which still 

 shows the cephalic fissures. The ducts do not, however, open out into these fissures, but 

 just above them. This also proves how far the fissures reach, all along the oesophageal 

 region. In the 410th section the end of the cephalic fissures may be said to be reached, 

 the whole of the nephridial system, excretory ducts and all, being thus situated within 

 the region of the fissures. 



Another specimen from the same locality was without a head, and though the 

 principal points of comparison are thus deficient, I feel confident, by the internal 

 characters which are shown by the sections, that we may look upon this specimen as 

 belonging to the same species. It was exceedingly well preserved and showed certain 

 interesting points with regard to the generative organs, which will be more fully discussed 

 in the paragraph devoted to those parts. 



Another feature by which the species is — if not distinguished from its neighbours — 

 at least characterised as far as the fragments allow us to judge, is the great thickness 

 of the transverse connecting vessels between the medio-dorsal vessel and the two lateral 

 ones. 



Cerebratulus corrugat us (M'Intosh), Hubrecht (PI. I. fig. 17 ; PI. XI. fig. 9 ; PI. XI h 

 figs. 3, 4 ; PI. XIII. figs. 1-6 ; PI. XIV. figs. 2-4). 



This species, which was first described by M'Intosh in the Transactions of the Royal 

 Society for 1879 (extra vol., p. 262), has again been recognised by this author as occurring 



(ZOOL. CHALL. EXP. — PART LIV. 1886.) Hhh 6 



