1 42 McMURRICH. [Vol. V. 



not yet developed tentacles. The mouth is at the smaller ex- 

 tremity, and the oral half of the body is to a greater or less 

 extent folded within the aboral portion in the preserved in- 

 dividuals, the ring of cilia lying at the bottom of the groove 

 so formed (Fig. 5). In this contracted condition they measure 

 about 1.4 mm. in length and 1.5 mm. in diameter. A transverse 

 section passing through the stomatodaeum of one of these is 

 represented in PL IX, Fig. 6, and it will be seen that there are 

 present in all twelve mesenteries. Of these, six, those num- 

 bered I, II, III, are perfect, while the other six, of almost equal 

 length, are quite small. The numbers assigned to the various 

 mesenteries indicate their probable order of appearance, the 

 ventral directives (III) being probably the third, and the dorsal 

 directives (IV) the fourth pair to be developed. The stomato- 

 daeum is elongated in the usual direction, and the single siphono- 

 glyphe (Si) is already evident. 



The older specimen was cylindrical in shape, with a well- 

 marked base, and its ring of cilia had disappeared. It measured 

 about 2.5 mm. in length, and 1.3 mm. in diameter. A number of 

 tentacles, apparently about twelve, though it was impossible to 

 determine the exact number, had made their appearance. Un- 

 fortunately, the specimen was somewhat macerated as well as 

 distorted, so that it was impossible to make out satisfactorily 

 the histological details, and camera drawings of single sections 

 do not present a clear idea of the arrangement of the mesen- 

 teries, though this can be readily ascertained by a study of 

 several serial sections. The figure I have given (PL IX, Fig. 7) 

 is slightly schematized, the section from which it was drawn 

 having been imperfect, but it represents truly the actual rela- 

 tions of the parts. The stomatodaeum has been considerably 

 distorted from its proper shape, but the position of the siphono- 

 glyphe is clearly indicated. The six pairs of mesenteries seen 

 in the younger stage are readily recognizable (I-IV), and pre- 

 serve their original relations to the stomatodaeum ; but in addi- 

 tion to these, four mesenteries, arranged in pairs (1-2), have 

 made their appearance in the exoccels upon either side of the 

 ventral directives. Of these new mesenteries, the dorsal pair 

 upon the right side (ir) is somewhat more developed than the 

 others, the ventral member of the pair having reached the 

 stomatodaeum. 



