10 A MONOGRAPH OF THE 



of the animal kingdom. They further express an opinion that the facts upon which is founded 

 the doctrine " that the form of the body and the internal organisation are independent of each 

 other," are not real, and that that hypothesis cannot be any longer maintained. 



Prior to the appearance of these reports, a series of very excellent papers had been 

 published by M. Milne Edwards, taking an extended review of the circulatory system in the 

 Mollusca. He states his conviction, founded on extensive researches undertaken for the 

 purpose, that the venous system is incomplete throughout the whole of this large division of 

 the animal kingdom. In all instances he finds the true veins more or less imperfect, their 

 place being supplied by a series of lacunes, and the blood in most cases also flowing into the 

 abdominal cavity. The condition of the Nudibranchs he does not consider to be exceptional. 



The difference of opinion amongst these distinguished naturalists with respect to the 

 circulatory system, has resolved itself into a very subtile anatomical fact. Both parties admit 

 the existence of large cavities into which the blood flows, but, on the one part, they are 

 considered as mere expansions of the vessels into blood-sinuses, and hence the vascular 

 system is uninterrupted ; while on the other, they are held to be lacunes or gaps in the 

 continuity of the vessels, showing a yet imperfect state in the structure of these organs, and thus 

 forming an intermediate stage in the development of the vascular system, between its first 

 imperfect appearance in the lower animals, and the complete system of closed vessels, only to 

 be found, according to M. Milne Edwards, in the Vertebrata. 



A very elaborate monograph of a species of Tergipes, found on the shores of the Black 

 Sea, was submitted to the Academy of St. Petersburg, by Professor Nordmann, of Odessa, in 

 1844, and appeared in the 'Annales des Sciences Naturelles,' in 1846. M. Nordmann' s view of 

 the digestive and circulatory systems appear to agree pretty nearly with those of Messrs. Milne 

 Edwards and De Quatrefages. The liver, however, he had entirely misunderstood. He had 

 observed auditory capsules and otolithes, and that the ovate vesicles of the papillae occasionally 

 discharge " a kind of mucus." He gives a full account of the embryology, and has traced the 

 ulterior development of the young animal further than had been done by other authors. 



It is unnecessary here to analyse many excellent essays on the Nudibranchiata that 

 appeared nearly contemporaneously with or subsequent to those already mentioned, evincing 

 the interest that these little mollusks had excited among European naturalists. The papers of 

 Professor Allman ' On the Anatomy of Actceon, with remarks on the PMebenterata? and of Dr. 

 John Reid ' On the Development of the Nudibranchiate Mollusca,' in the 'Annals of Natural 

 History,'* and those of M. E. Blanchard, { Sur l'Organisation des Opisthobranches/ in the 

 'Annales des Sciences Naturelles,'t may be cited as affording many interesting details of 

 anatomy and development. So far as these authors touch upon the question of Phlebenterism, 

 their opinions are generally more or less opposed to those of M. de Quatrefages. In a paper 

 on the ' Anatomy of Doris ' by Mr. Hancock and Dr. Embleton, read at the Edinburgh 

 Meeting of the British Association, in 1850, and since published in a much enlarged form in 

 the * Philosophical Transactions of the Royal Society,' a portal heart and a sympathetic system 

 of nerves were shown to exist in the Nudibranchiata, being the first time that the existence of 

 these organs has been fully demonstrated in any of the invertebrated animals. • 



From this brief history of the study of these Mollusks it will be seen that many important 



* Vol. 16, p. 145, and vol. 17, p. 377. f 3d ser., vol. 9, p. 172, and vol. 11, p. 74. 



