24 THE MEDUSAE. 



the line of development of these three genera is impossible to determine 

 without studying their young stages. But the evidence afforded by the 

 adults suggests that such is the case. 



Periphylla Steenstrup, 1837. 

 sens. em. Vanlioffen (: 02 a ). 



Periphyllinae with 3X4 tentacles. 



The anatomical and histological structure of this, the best-known genus 

 of the family, has been so carefully studied, since Haeckel's ('80) description, 

 by Maas ('97, : 03, : 04 c ) and Vanlioffen ('92, : 02 a ), on satisfactory material, 

 that repetition here is unnecessary. 



The species described by Haeckel ('80) under the genera Peripalma and 

 Periphylla, and by Fewkes as P. humilis, have been successively reduced, 

 until Vanlioffen (: 02 a ) and Maas (: 04°) recognize only three: P. dodeca- 

 bostrycha Brandt, '38, P. hyatinthina Steenstrup, '37, and P. regina Haeckel, 

 '80. The considerable number of specimens taken on the expedition of the 

 " Vaklivia" and those of the Prince of Monaco have afforded ample opportu- 

 nity to these two students to make careful comparisons between these three 

 species. Mayer (: 06), on the other hand, argues that P. dodecabostrycha 

 and P. hyacinthina are in reality synonymous, the differences in form of the 

 bell and in extent of pigmentation being, according to his view, the result 

 merely of different stages in growth, or of individual variation. This view 

 has much to recommend it; and although I realize that further studies on 

 more extensive series of the two forms must be made before any final con- 

 clusion can be reached, I think it wisest to accept it provisionally, even 

 though it be sharply opposed to the opinions of two such eminent authorities 

 as Maas and Vanhdffen. In support of the thesis that the two species are 

 identical I may cite the following important observations on the part of pre- 

 vious si iidents. So Ear as I can learn, no specimen of /'. hyacinthina, showing 

 the characteristic form and pigmentation, has been recorded smaller than 35 

 mm. high, or than 21 mm. in diameter. On the other hand, we know, from 

 recent studies a! least, of no specimen of /'. dodecabostrycha larger than 27 mm. 

 high, or than IS nun. in diameter. Furthermore, no typical specimen of 

 /' hyacinthina has been observed without well-developed gonads, although such 

 specimens have been recorded several times for /'. dodecabostrycha. Considering 

 ho« many individuals of the two BO-called species have been examined, this 



erj Btronglv in favor of their identity . 



