HISTORY OE THE SUBJECT. 29 



Many valuable remarks occur in the article on Tetrastemma ohscurum concerning the proboscis, 

 the development of the stylets, the position of the mouth, the digestive and circulatory systems. 

 He over-estimated the relation of the marginal stylets to the central, for he thought that the former 

 supplied new organs to the latter. He also confounded the circulatory with a water- vascular 

 system. He, however, exhibits great care and accuracy in his observations, which put Nemertean 

 anatomy on a sounder footing than it had hitherto held. 

 He divided the Turbellaria into two sub-classes, thus : 



Classis Turbellaria. 

 I. Sub-classis Aprocta. 



1. Ordo Dendroccela. 



2. „ Rhabdoccela. 



II. Sub-classis ProctucJia. 



1. Ordo Arhynchia. 



2. „ Rhynchoccela (Nemertina). 



This classification has been adopted by Dr. Rud. Leuckart in the appendix to Van der 

 Hoeven's ' Handbuch der Zoologie. 5 



Dr. Thomas Williams, in his 'Report on the British Annelida,' at this time 1 propounded 

 several erroneous statements in relation to the anatomy of the Nemerteans. Thus, while 

 correctly regarding the sacculated chamber as connected with the digestive system (though he 

 denied the existence of an anus), he called the ganglia "hearts," and wrongly averred that the 

 " oesophageal intestine " (proboscis) terminated in a distinct papillose outlet situated a short 

 distance behind the cephalic extremity of the body, as in the Sipunculidae. His attempt to prove 

 the homology between his " closed alimentary chamber " and the spongy mass in Taenia rests 

 upon no secure foundation, and does not stand the light of the correct investigations of that 

 period or the present ; and the same remark applies with respect to his grouping Gordius with 

 the Nemerteans. 



An interesting addition to our knowledge of the development of the group was made 

 by Dr. W. Busch, who at this stage gave a drawing and description of a novel animal 

 from the harbour of Trieste, on which he bestowed the name of Alardus caudatus? This is 

 evidently the young of a Micrura, and J. Miiller afterwards connected its growth with that of his 

 Pylidium. Dr. Busch termed the aperture of the proboscis the mouth, did not recognise the 

 proboscis (though its position is indicated in his figure), and was puzzled by the cephalic sacs, 

 which, as usual in the young of the Anopla, were very large. 



Dr. Thos. Williams in 1852 again introduces the subject of the Nemertean "chylaqueous 

 fluid/' in his paper "On the Blood-proper and Chylaqeous Fluid of Invertebrate Animals." 3 

 Here he also confounds the corpuscles in the proboscidian sheath with the contents of his 

 " alimentary caeca." 



1 < Report of the Brit. Assoc./ 1851, pp. 238, &c, pi. xi. 



2 ' Beobachtungen uber Anat. u. Entwickelung einiger wirb. Seethiere/ Berlin, 1851, p. Ill, 

 taf. xi, f. 8. 



3 ' Philos. Transact./ 1852, part ii, p. 627, pi. xxxii, f. 25. 



