

BUDDING PROCESSES OF CEPHALODISCUS DODEGALOPHUS. 513 



On the other hand, the similarity of the gonads of Cephalodiscus to those of 

 Balanoglossus is patent. They differ mainly in the fact that, as in the case of the 

 pharyngeal clefts, there is only a single pair. 



Nervous System and Pedicle. (Ventral Sucker.) 



In a former paper already referred to, the nervous system was described as 

 consisting of a dorsal ganglion over the sub-neural sinus, a pre-oral ring, a post-oral 

 ring, and a pair of lateral nerves down the trunk. In addition, there are nerves to each 

 of the plumes. 



Fig. 85 is a diagram giving the distribution of the main nervous tracts, though the 

 more or less general nervous plexus is not indicated. In the mid-ventral line of the 

 trunk, from the trunk backwards, there passes a broad nervous tract which can be 

 traced directly into the pedicle. The lateral nerves can be followed into the same organ. 



Fig. 18 shows a transverse section of the pedicle. In the mid-ventral line may be 

 seen the ventral nerve (v.n.) cut in section and forming a long ridge, with the chondroid 

 layer between it and the coelome. On each side is a lateral nerve (v.l.n.) similar 

 in appearance but not so prominent. In all these nerves there can be discerned a fine 

 lumen which is more or less continuous throughout the pedicle. The three nerves 

 gradually approach towards each other till at the tips they become indistinguishable. 



Immediately inside the ectoderm is a fairly thick layer of chondroid tissue, and 

 internal to it, is a well-defined layer of longitudinal muscles (l.m.). The ccelomic space O 



in the middle is directly continuous with the trunk-cavities, and the dorsal and ventral 

 blood-vessels are direct continuations of the similar vessels in the trunk. 



The main difference between the structure of the pedicle and that of the trunk is the 

 absence of endodermic elements (intestine) in the former. The acknowledged secondary 

 character of a reduplicated gut leads one to conclude that the pedicle is morphologically 

 the hind end of the body, and that the actual posterior sacculated part of the animal is 

 a secondary dorsal protuberance. A basal fixative portion of the body in Phoronis can 

 be shown on similar grounds to be the true hind end of the body, and therefore 

 homologous with the pedicle of Cephalodiscus. It will be seen later that this interpre- 

 tation of the pedicle agrees with its relationships as seen in the buds. 



Sexual Reproduction. 



In going over a series of specimens mounted by the late Professor Busk, and now in 

 the possession of Professor M'Intosh, I was struck by the appearance of an adult, which 

 I have figured here (fig. 86). 



It will be noticed that in the cloacal region there is a group of cyst-like structures 

 closely pressed together and having a resemblance to a number of larvae enveloped in 

 their egg-capsules. 



