ON DEVELOPMENT ETC. OF THOtlONlS. ÔÔi 



jMasteeman says iiotliiug of the method (■iii[)l()y('d in liis inves- 

 iiiratioii, ami uiitortuiiati'lv there exists no other study lliaii his 

 with wliich lo eoiiii)ai"e mv resiüts. 



As mav l»e gathered from the ai)ove-meiitioiicd figure, I eau 

 discover no collar nerve ring, nor dorsal or ventral eounnissui'e. 

 Besides, in spite of repeated efforts, I have always failed to make 

 out the presence oi the so-called perianal nerve ring. The collar 

 ring and the dorsal commisure, if they can Ije s(j named, are repre- 

 sented by a small number of parallel fibres, which spring directly 

 out from the posterior corner of the nerve ganglion. In evei'y 

 case examined, they could be traced no further than a short dis- 

 tance from the ganglion. Sometimes, I ha\e Ijeen al)le to discern 

 in sections the main nerves (commonly 3 in number), which run 

 close together and parallel to one another along the mid-dorsal 

 line of the trunk, 1)ut they were confined to only a few sections 

 posterior to the first pair of tentacles. On the other hand, a 

 vei'v complex and l:)eautiful system of nerve iiljres could be seen 

 on the preoral lobe. The fibres are here exceedingly numerous 

 and fine, radiating from the ganglion on all sides towards the 

 free margin of the preoral lol)e. In the median line and 

 anteriorly to the ganglion (r/l.), th(! fibres appear as three longi- 

 tudinal })arallel strands on Avhich the unpaired sensory spot (so.) 

 is situated not far from the ganglion. After passing through the 

 sensory spot the strands fray out into fnie fibres which continue 

 their c(jurse towards the free margin of the preoral lobe. The 

 fibres emanating iVom the ganglion do not all show a regular 

 radial arrangement, but there are some that aiisiug from the 

 lateral edge of the ganglion, soon take an anteriorly directed course. 

 Sometimes there were not wanting, especially near the ganglion, 

 indications of anastomosis between the fibres. H(jwever, it seemed 



