(CuviER, VAN Beneden, Souleyet and Gegenbaur), as Pelseneer already gave a criticism about 

 them. For conciseness' sake, I believe it will be better to omit the facts, already known; and 

 so I shall confine mjself to a few remarks on the nervous system, in which I do not agree 

 with Pelseneer's description ^). 



The nervous system of the Pneumonodermatidae is chiefly characterised by : 

 i" the rather long connectives, the result of which is that the various ganglia are distinct, and 



not fused together. 

 2" the asymmetry of the visceral ganglia (the right is the smaller one), also expressed in the 



nerves proceeding from them. 

 3" the second anterior pedal commissure. 

 4° anastomosing nerves. 

 I. The cerebral ganglia are rounded in Pneumonoderiua (PI. V, fig. 124, r), transversely 

 elono-ated with distinct commissure in Spongiobranchaca, quite as Pelseneer already affirmed. 

 The connectives b\- which they are connected with other ganglia have been exactly 

 described by Pelseneer ; in my figure the buccal connectives are not indicated, in order to avoid 

 complication. The cerebro-pedal (a), and the cerebro-pleural connectives (<5) are, however, visible. 

 A large number of nerves issue from the cerebral ganglia. First the posterior 

 tentacle is innervated by two nerves, the lateral and posterior of which (i) is the optic nerve, 

 exhibiting an elongated ganglionic swelling at its base. The second nerve, more medial and 

 anterior (2) is the olfactory nerve. Both these nerves terminate in ganglionic swellings, almost 

 juxta-posed, and a little before these ends an anastomosis comes between them, which shows 

 etpially an elongated enlargement. Souleyet whose figures ~) are by far the best among all 

 those of former researches, has not seen this anastomosis, but it was discovered by Boas'). 

 Ventrally to the origin of the optic nerve a slender nerve (3) passes to the otocyst. 

 This innervation was seen by Pelseneer ^) in Spongiobranchaca. 

 From the anterior part of the cerebral ganglia arise: 

 i" a rather strong nerve (4) to the labial tentacle. In Sp07igiobranchaea, which has, as 

 one knows, the anterior tentacles well developed, the innervating nerve is stronger, 

 conformable to this circumstance. 

 2" a complex of three nerves (5 — 7), the function of which I could not clearly make out. 

 This complex, however, innervates (according to Pelseneer) the proboscis, the lips 

 and the buccal appendages. A common trunk from which two or perhaps the three 

 nerves arise, I could not observe. Pelseneer declares that the nerve to the anterior 

 tentacle proceeds from a common trunk with another nerve to the buccal appendages, 

 but I must deny the truth of this, also with respect to Souleyet's statement ") ; besides, 

 these two authors have not seen one of the two nerves (from the anterior side of 

 the cerebral ganglia) which arise near the median line. 



I) Op. cil., p. 41— 45i pl- l^'i % 9, pl- '^'t figs- 1, 3- 



i) Voyage de la Bonite, voL IL P- 26S, pL XV, figs. 29, 30, 32, 34, 35. 



3) Spolia ailantica. 



4) Op. cit., p. 42, pL V, fig. 3. 



5) Op. s. c, p. 268, pl. XV, figs. 30, 33. 



