ROSÉN, STUDIES ON THE PLECTOGNATHS. 19 



IV. Notes 011 otlier parts of the intestiiies. 



As regards the other parts of the intestines I shall con- 

 fine my inquiry to a few notes. The material at my dispo- 

 sal does not allow of a more detailed description. The liver 

 has already been mentioned. In Balistes it is large and bilo- 

 bate, reaching almost to the anus. It occupies the place be- 

 tween the intestine and the ventral body wall. In Dzod^on and 

 Spheroides, this organ is comparatively reduced, forming a 

 thick rounded mäss on the right side. A gal! bladder is 

 present. The pyloric caeca are wanting in all species I have 

 examined and they are not recorded from any others. The 

 intestine (s. str.; the part between the stomach and the anus) 

 forms several coils. (Figs. 3 and 7.) In Balistes there are 

 folds forming a network on its inner surface. In Spheroides 

 the folds are longitudinal. No glands are present. There is 

 an interiör circular muscle-layer and an exteriör longitudi- 

 nal one. 



V. Pliylogeuetical Remarks. 



The alimentary canal and its deri vätes af förd no oppor- 

 tunity for a discussion on the place of the Plectognaths among 

 the other Teleosts. The air-sac is developed within the group. 

 The liver varies much in different orders of Teleosts, and 

 the same is the case with the glands, the folds on the inner 

 surface of the intestine and the pyloric caeca. But, on the 

 other hand, the air-sac which is characteristic of so many 

 Plectognaths forms a good base for a study of the develop- 

 ment within the group. The Molids and the Ostraciontids 

 which possess no such sac, must have developed independently 

 of the other families. The inquiry given above on the air- 

 sac has clearly shown that we have every reason to believe 

 that the families Triacanthidae, Balistidae (including the genus 

 Monacanthus), Diodontidae and T etrodoniidae form a conti- 

 nuous series of development. This is an evident proof a^am^^ 

 the present classification of the Plectognaths into two sub- 

 groups, Sclerodermi and Gymnodontes, as proposed by Regan. 



