34 HISTORY OF THE SUBJECT. 



By his first great division, "based on the presence or absence of the ventral aperture (by 

 which he probably means the mouth), the Enopla are in a rough way separated from the 

 Anopla, but the classification, being founded on external characters, fails just where it is most 

 wanted. The author considerably extends the limits of the known species, and gives an 

 interesting chronological list of the genera. 1 



Dr. E. Graeffe 3 next furnishes an account of a yellowish-green Tetrastemma from Nice, 

 which is remarkable in having lenses to its eyes, and in possessing what he terms otolithes. The 

 presence of the latter organs, if no misconception occurred, is something very different from 

 anything seen by us in the British Nemerteans, but is analogous to the otolithes described by 

 several authors in other invertebrates, such as the Mollusca. 



Dr. Thomas Williams, in a morphological paper, published in 1858, committed some serious 

 errors in his interpretation of the Nemertean generative organs, which, he said, coincided in 

 shape, place, and structure, with the ovarian or female series of the Hirudinei. 8 Moreover, he 

 asserted that they corresponded in number not with the caeca of the alimentary canal, but with 

 the annuli of the body, a statement requiring some further proof, since it is very doubtful if the 

 term annuli can be used in any sense with respect to the Nemertean body, which is not in truth 

 segmented. His representation of the ovaria or female segmental organs in Folia quadrioculata 

 is imaginary, for the organs are reversed, made bifid at one end, and filled with minute cells, — 

 conditions at variance with nature. He thought that the Nemerteans should be separated from 

 the Planarians by a very wide interval ; indeed, he affirmed that they had only one character in 

 common, viz. the ciliated integument. This cannot be supported in the sense he means, though 

 the gap between the two is by no means narrow. 



Gegenbaur 4 the following year arranged the Nemerteans under the sub-class Platyel- 

 mintkes, order 3, Turbettaria Rliynchoccela. He followed De Quatrefages in regard to the 

 general anatomy of the animals. 



Schmarda at this time described many foreign Nemerteans, which he had collected during 

 his voyages, in a finely illustrated work. 5 He divided the order Nemertinea into two sub-orders— 

 based on the absence or presence of the " respiratory organs," and termed respectively Abranchiata 

 and Bhochmobranchiata. The former he portions into families according to the shape of the head ; 

 the latter is similarly divided, in conformity with the number of the supposed branchial furrows or 

 fissures. He gave the opinion, in his introduction, that the structure of the stylet-region of the 

 proboscis might be of service in classifying the smaller species, but was utterly useless in the 

 larger forms, and those preserved in museums, hence he was obliged to take the former mode of 

 discrimination. But it is impossible to study such animals with any degree of accuracy as spirit- 

 preparations, without first having investigated them as living subjects. It is unnecessary to give 



1 C( 



Prodromus descriptions Animalium Evertebratorum, quse in Expeditione ad Oceanum Pacificum 

 Septentrional em, a Republica Federata missa/' &c, part ii, Turbellarieorum Nemertineorum ; "Proceed. 

 Acad. Nat. 8c./ Philadelphia, 1858, pp. 159—165. 



2 ' Beobachtungen iiber Radiaten u. Wiirmer in Nizza/ pp. 53 and 54. Zurich, 1858. 



3 "On the Structure and Homology of the Reproductive Organs of the Annelids/' 'Philos. Trans./ 

 1858, pp. 131—132, pi. 8, f. 24. 



4 ' Grundziige der Vergleichenden Anatomic' Leipzig, 1859. 



' Neue Turbell., Rotat. u. Anneliden beobachtet u. gesammelt auf einer Reise urn die Erde, 1853 

 bis 1857/ i, 1; Introd., pp. xiii and xiv, and pp. 40—46. taf. 9—11. Leipzig, 1859. 



