STEUCTURE, ETC., OP OERATA OF NUDIBRANCHS. 47 



The cerata of Dendronotus have been generally described 

 as branchiae, and have been universally supposed, until quite 

 recently, to contain large digestive caeca or diverticula of the 

 " liver." I regard them, however, as being merely excessive 

 developments of the small cerata found in Tritonia, and as 

 having no special branchial function ; while last summer Mr. 

 Clubb and I showed ^ that no digestive caeca penetrate into the 

 cerata in Dendronotus. Such caeca were described and 

 figured originally by Alder and Hancock,^ and more recently 

 by Dr. R. Bergh,^ but these distinguished anatomists worked 

 entirely, I believe, by means of fine dissections, and I can 

 explain, I think, how it is that a deceptive appearance of 

 hepatic diverticula is produced which has led to error when 

 not corrected by the examination of serial sections. 



The so-called liver is a very large organ lying underneath 

 (ventral to) the ovo-testis. It consists of a posterior and right 

 and left anterior lobes, as correctly described by Bergh. It 

 gives ofi" a few diverticula directed dorsally, but these do not 

 reach to the bases of the cerata, but end blindly in the body- 

 wall. In the specimens examined by Mr. Clubb and myself 

 last summer we found such prolongations going towards the 

 rhinophores and the two first pairs of cerata, and sometimes, 

 but less definitely, towards the smaller succeeding cerata, but 

 in no case, either in dissections or in sections, were they found 

 to reach the base either of rhinophores or of cerata. 



Dissections alone are apt to be misleading, as there are large 

 blood sinuses (a) in the side walls of the body close to the liver 

 and (b) extending up into the cerata, and these cavities join and 

 open into the dorso-lateral veins close to where the hepatic 

 diverticula terminate, so that it is easy to imagine a direct con- 

 tinuity between the slender end of the diverticulum and the 

 blood sinus and so proceed to trace the supposed hepatic caeca 

 onwards into the cerata. In serial sections, however, the pro- 



1 'Proc. Liverpool Biol. See.,' vol. iii, p. 228, 1889. 

 - ' Ray Soc. Monograph,' pt. ii. 



3 " Bijdragen tot de Dierkuude," * Natura Artis Magistra,' Afl. xiii, viii, 

 p. 25, Amsterdam, 1886. 



