8 Catalogue of Chaetopoda 



cylindraria [Pectinaria], Nereis conchilega \Lanicc\, Nereis lutaria 

 [a Sabellid], Serpula, and Lumbricus echiurus \Echiurus\, and in 

 1788 there appeared a further series of his studies x on various 

 " Nereis" including " Nereis lumbricoides " [Arenicola marina], and 

 some tubicolous worms [including Spirorbis]. 



Up to the time of Pallas, and, indeed, for a considerable period 

 subsequently, the tubes of Serpula were described and figured in 

 works on conchology 2 along with the more loosely coiled gastropod 

 shells ; but Pallas showed in his earlier paper 3 that the shell of 

 Serpula is different from that of the true Testacea, that Serpula 

 agrees fundamentally in structure with Nereis and Aphrodite, with 

 which it should be united to form an order, in which should also be 

 placed the genera Lumbricus, Hirudo, Ascaris, Gordius, and even 

 Taenia. Pallas was thus the first to recognise some of the essential 

 differences between worms and molluscs. 



Otto Friedrich Miiller 4 and Otto Fabricius 5 successfully 

 elaborated the systematic details regarding worms of various kinds, 

 devoting much care to the distinction and definition of genera and 

 species. Miiller founded the genera Amphitrite and Nais, and did 

 much to clarify the diagnoses of previously established genera of 

 worms. His classification of the Vermes (1776) the class having 

 the limits defined by Linnaeus is well worthy of notice. He 

 divided the class as follows : 



1. Infusoria [animals living in infusions] . 



2. Helminthica. 



3. Mollusca [similar to the order Mollusca of Linnaeus, except that the 



genera Aphrodita and Nereis were transferred to the division 

 Helminthica] . 



4. Testacea [corresponding to the Testacea of Linnaeus] . 



5. Cellularia [corresponding to the Lithophyta and Zoophyta of Linnaeus] . 

 The Helminthica found in Denmark and Norway were subdivided into two 



groups : I. Mutica, containing Gordius, Ascaris, Echinorhynchus, 

 Hirudo, Taenia ; II. Setosa, containing Lumbricus, Nereis, Amphi- 

 trite, Nais, Aphrodita. 



This classification marks a distinct advance on that of Linnaeus, 

 showing good progress in the direction of a separation of worms and 

 molluscs. Muller's order Helminthica contains worms only. There 



1 Nova Acta Acad. Sci. Imper. ii, 1784, Petropoli (1788). 



2 See, for instance, d'Argenville's Conchyliologie, Paris, 3 Edit., vi (1780), 

 tab. Ixviii. 



3 Op. cit. (1766), p. 74. 



4 Vermium Terr, et Fluv., Havniae, i (1773), pars i : pars altera (1774) ; 

 Zool. Dan. Prodr. (1776). 



5 Fauna Groenlandise, Hafniae (1780). 



