124 THE VOYAGE OF H.M.S. CHALLENGER. 



tentacles are also of two sizes, arranged alternately, but here there are twelve of eaeh 



si/e. 



In ( 'ideal us ■perlucidus and Culeolus moseleyi the relative sizes and arrangements are 

 not so definite. In the latter species the tentacles are small, and are the simplest and 

 least branched forms found in the genus. 



The Dorsal Tubercle. — This organ in Culeolus murrayi and Culeolus toyville-ihom- 

 soni has quite the ordinary structure, and resembles the simpler forms we usually find in 

 the Cynthiidse. In Culeolus moseleyi also the dorsal tubercle is not abnormal, having an 

 ovate form, an aperture, and two twisted horns. 



In two of the species, however, Culeolus recumbens and Culeolus perlucidus the organ 

 is very different, and is apparently of a much simpler type. In both it takes the form of a 

 somewhat elhptical mass with a simple straight aperture — merely the opening of the canal 

 provided with thick lips, and not twisted or coiled in any way. In Culeolus perlatus I 

 was unable to make out the dorsal tubercle without cutting the unicpie specimen more 

 than I considered justifiable. 



There is nothing notable about the nerve-ganglion. It occupies the usual position, is 

 of elongated form, and gives off nerve trunks at the branchial and atrial ends. 



I was unable to make any observations on the condition of the neural gland. From 

 want of material I could not make a special object of this organ, and it was not noticed 

 incidentally along with any other parts. In Culeolus recumbens and Culeolus perlucidus, 

 however, where the region of the nerve-ganglion and the peritubercular area were carefully 

 examined, it cannot have any great development ; and it probably constitutes the mass 

 forming the back of the dorsal tubercle, in which case the canal leading from the gland to 

 the tubercle would be reduced to a minimum. 



There is nothing worthy of special remark in the condition of the peripharyngeal 

 bands, the praebranchial zone, and the peritubercular area. 



Hie Alimentary Canal. — The structure and course of the alimentary canal was 

 determined in those species of which there are more than a single specimen. 



In all it is small relatively to the size of the body and compared with the branchial 

 sac ; and in all it is situated at the posterior end of the body and on the left side of the 

 branchial sac. In all the oesophagus is short, the stomach large and well defined, and 

 the intestine long and narrow, but here the general simdarity ends. 



In Culeolus murrayi the anterior or intestinal end of the stomach is rather the 

 larger, while in Cideolus recumbens the oesophageal end is the larger. In both the wall 

 is pushed out into a number of csecal processes or diverticula. In Culeolus perlucidus 

 the stomach is more elongated, tapers towards both ends, and has no csecal processes. 

 Though the exact course of the intestine differs in the three species, yet in all it runs 

 for a short distance anteriorly along the ventral edge of the branchial sac, after leaving 

 the stomach, and then turns dorsally, up the left side, and finally runs back posteriorly 

 fco end near the atrial aperture. 



