clxxxiv GENERAL SUMMARY OF SCIENTIFIC AND 



the papers, finely illustrated, of Mr. Macintosh, upon the 

 structure of the Nemertian worms, while his work on the 

 worms of Great Britain has been issued by the Ray So- 

 ciety. 



Dr. Ilabrecht has described a number of new genera and 

 species of these worms, and drawn attention to the minute 

 structure of the nerve-ganglia. Haemoglobin was detected 

 by means of the spectroscope in the nerve-tissue of two spe- 

 cies of Meckelia and in true red blood-disks of Drepanopho- 

 rus. He has also noticed the formation of an invasrinate 

 gastrula in the early stages of JSorlasia olivacea. 



In last year's report we noticed the work of M. Villot on 

 the structure and development of the Hair-worm (Gordius). 

 He finds that the young Gordhis aquaticus first makes its 

 way into insect larvae, such as C/iirotiomus, and becomes 

 encysted ; after which it finds its way with its host into the 

 alimentary canal of fishes, where it is again encysted. It 

 escapes from this position in the spring. 



Further researches on the ascidians by Ussow bring him 

 to the conclusion that the Tunicates are not Mollusca. 

 "Even," he says, "without taking into consideration the 

 modes of embryonal development, a comparison of the plan 

 of structure of the different mollusca with that of the Tuni- 

 cata suffices to refer the latter with more propriety to the 

 Vermes. The simple cardiac tube, the absence of the oesoph- 

 ageal ganglia and their commissure, the complete absence 

 of the foot, the curvatures of the intestinal canal directed 

 toward the heart, the existence of the outer mantle, and the 

 peculiarities of its structure, mode of formation, and chem- 

 ical constitution, the variability in the direction of the con- 

 tractions of the cardiac tube, etc., all draw a more or less 

 sharp boundary-line between the Tunicata and the Mollusca. 

 The Tunicata approach most closely to the Bryozoa." On 

 the other hand, he points out important characters in which 

 the Tunicates approach the worms ; while from the presence 

 of a chorda dorscdis, the type of development of the cen- 

 tral nervous system, and the relation of the alimentary tube 

 to the bronchial sac, the Tunicata are related to the Verte- 

 brata. Ussow goes so far as to adopt Oscar Schmidt's view, 

 according to which the Tunicates form a sj>ecial class of 

 Protovertebrata. 



