140 HUGH WATSON. 



otocysticns, altliough I was unable to find the otocysts 

 themselves even in sections of the pedal ganglia. Lastly, a 

 slender nerve arises from each ganglion between the two 

 connectives, usually neai-er to the cei-ebro-pleural connective 

 than to the other. In Apera dimidia, A. pur colli, A. 

 burnupi, and A. sexangula these nerves ruii back to the 

 anterior end of the buccal retractor, which they innervate. 

 Each gives off two branches close to the cerebral ganglia ; 

 one of these anastomoses with the cerebro-buccal connective 

 not far from its origin ; the other runs down between the 

 cerebro-pedal and cerebro-pleural connectives, and divides 

 into two about half way to the ventral group of ganglia. 

 One of the divisions of this branch leaves the nerve collar 

 and innervates the retractor of the lower tentacle.^ The 

 other division continues down to the ventral ganglia ; but 

 whether it fuses with the pleural ganglion, as one might expect 

 from Amaudrut's observations," or whether it merely crosses 

 the dorsal surface of the ventral group of ganglia and leaves 

 it again in the wall of the buccal artery, I was unable to 

 discover with the limited amount of material at my disposal. 

 The examination of these slender nerves, deeply embedded 

 amongst the connective tissue and blood-vessels which 

 surround the larger nerve-cords and ganglia, is a matter of 

 considerable difficulty ; but it does not even requii-e a com- 

 pound microscope to see that the anterior end of the buccal 

 retractor in A. dimidia, A. sexangula, and their allies is 

 innervated by nerves arising from the sides of the cerebral 

 ganglia. This is one of the very few respects in which 

 Apera resembles Daudebardia more than any other 

 carnivorous genus with which I am accpiainted.^ In A . 

 gibbon si the buccal mass with the odonrophore is much 



1 In Natalina quekettiana (M. & P.) and Rhytida capillacea 

 (Fer.) the i-etractors of the lower tentacles are also innervated hj very 

 slender nerves issuing from the nerve-collar about half-way down each 

 side, and this is prol^ably the case in several other forms as well. 



» ' Ann. Nat. Sci., Zool.,' 1898, vol. vii, pp. 123-126. 



3 See Plate, L. H., ' Zool. Jahrb.,' 189], vol. iv. p. 591. 



