Protostigmata in ascidians

It has been showed that at a certain stage in the ontogeny of Ascidians there is usually a definite number of stigmata or gill slits, which are elongated dorsorventrally and arranged in a longitudinal series on each side of the pharynx. To these the name protostigmata was given by Garstang in 1892. The stigmata of the adult differ from these in being usually very numerous, indefinite in number and elongated antero-posteriorly. In 1904 Julin and Damas made two separate proposals to base the classification of the Tunicates on the condition of the protostigmata. As these proposals differed rather widely from each other and from the current classifications based upon the adult condition, I have taken up the question as far as it conerns the Ascidians and have investigated the origin of the stigmata in a large number of genera. I have been able to confirm for myself very many of the observations that have been published regarding the origin of the stigmata in the generaHolozoa [Distaplia], Clavelina, Ciona, Corella, Cæsira [Molgula], Botryllus andDendrodoa (Styelopsis) . In addition I have investigated the generaAmaroucium, Polycitor [Distoma], Sycozoa [Colella], Ascidiopsis (very nearAscidiella andPhallusia , which have been studied by others). The last three genera belong to the family Tethyidæ [Cynthiidæ], no members of which have been previously investigated as to the origin of the stigmata.