510 



Cresswell Shearer 



Material and Metliods. 



The material iised in the present work was obtaiued partly at 

 Plymouth, England, and partly from the small Pantano near Faro, 

 Messina. The Faro iarvae probably belong to the species Ph. psam- 

 mophila^ but their identity iì< not certain. Two distiuct Aetinotrocba 

 Iarvae are found at Faro at different seasons of the year, so that in 

 the Pantano there are at least two species of the adult worm. 1 

 bave been able to iind ouly one of these, which seems to resemble 

 Ph. psammopkila very closely. The other may be Pl>. kowaleiskii 

 the young- stages of which are at present unkuown. 



It is note-worthy that while in the Plymouth species, Ph. hippo- 

 crepùi, ali stages up to the free-swimming stage are frequently found 

 in the tentacles of a single adult, in the Sicilian species on the 

 other band ali the Iarvae found in the tentacles of one worm are 

 ali at the same stage of development. The Faro Iarvae are also 

 more difficult to raise, and I could never succeed in getting them 

 past the one tcntacle stage when raised from the egg; the Plymouth 

 Iarvae are readily reared to a later stage. The Faro Iarvae soon 

 cease to grow although at this time a large Aetinotrocba is very 

 abundant in the Plankton of the Pantano, and has been described 

 by Goodrich (11) as possessing 14 tentacles. 



I am greatly indebted to ^Ir. Marc de Selys Longchamps for 

 various stages of A. branchiata., which bave been of great service 

 to me. For fixing I bave found strong Flemmixg's and Hermanns 

 tiuid answer best. Sublimate gives poor results, at least for the 

 segmentation stages, causing the cells to assume a rounded and un- 

 natural shape quite unlike their appearanee when tìxed witbFLEMMiNo's 

 solution. With Sublimate-Acetic acid I bave obtained preparations 

 that resemble the drawings given by Ikeda (14) of the seg- 

 mentation stages of Ph. ijimai. For sections 1 bave used both the 

 ordinary Paraffin method and the modified Paraffin-eelloidin niethod. 

 For the study of whole mounts I bave found fresh material cleared 

 with acetic acid and glycerine, and stained with methyl green 

 very eatisfactory for temporary use. 



