478 Scientific Proceedings, Royal Dublin Society. 



single tentacle between each group. A deep siphonoglyphe, was 

 present, thus causing the mouth to be T shaped. The siphono- 

 glyphe, being in the axial line, indicates the disposition of the 

 tentacles. On reference to PI. XI., fig. 4, it will be seen that 

 the intermesenterial chamber on each side of the axial or directive 

 chamber is produced into a tentacle. Of the three remaining 

 lateral chambers, only the centre possesses a tentacle. 



All the previous accounts of the parasitic larva of Halcampa 

 agree in the fact of twelve tentacles being present. This can only 

 be accounted for by supposing that the larvae were more developed 

 than mine. This was certainly the case in Strethill Wright's 

 specimens, and in my oldest examples I found indications of the 

 sprouting of some of the missing tentacles. It is, of course, 

 possible that the Mediterranean form acquires its twelve tentacles 

 very early. 



Meyer and Mobius (Arch. f. Naturg., 1863, p. 70) mention that 

 in their adult examples of " Edwardsia duodeeimcirrata" Sars. 

 [Halcampa chrysanthellum], the number of tentacles varied from 

 eight to twelve, but never more than the latter number. 



By making a series of transverse sections I was enabled to trace 

 out the arrangement of the mesenteries in a more satisfactory man- 

 ner than could be effected by an examination of the living animal. 



In the oesophageal region, the twelve mesenteries appear to 

 have equal importance. The siphonoglyphe causes what may be 

 termed the ventral directive mesenteries to be much bent. At the 

 lower extremity of the oesophagus four of the mesenteries fall short 

 of joining the oesophagus. The siphonoglyphe extends for a short 

 distance beyond the oesophagus proper (PL XL, fig. 8). 



In the gastric region of the body there are eight large mesen- 

 teries, which alone bear the swollen digestive borders. It will be 

 noticed that it is those intra-mesenterial chambers, bounded by a 

 strong and a weak mesentery, which are not prolonged into ten- 

 tacles. The dorsal directive mesenteries also appeared somewhat 

 smaller than the remaining six. The same general arrangement 

 occurred at the posterior end of the body, except, of course, that 

 the mesenteries have no thickened edges. 



It is probable that at a slightly earlier stage only the eight 

 strong mesenteries are present, as an increase in the number of 

 tentacles with the growth of the animal is characteristic of most 



