. 546 



The fact that both the Petasma and the Thelycum differ in different 

 species has made them a useful part of the description of species, but 

 what they mean in the economy of the animals has not hitherto been 

 found out. 



In the Schizopoda, which are more primitive than the group of 

 Decapods, the Penaeidea; the male has likewise a remarkable complex 

 extension of the first abdominal leg, while the female has no peculiar 

 organ. S ars in the Challenger Reports, Vol XIII, p. 69, says: ,,As to 

 the function of these remarkable appendages in the male, there can, 

 I think, be little doubt of their serving to seize the spermatophores and 

 place them on the sexual openings of the female. The first pair are 

 unquestionably the most effective for this purpose, while the second 

 pair perhaps perform merely a coadjutory function." This conclusion 

 is based upon the fact that elongated pear shaped spermatophores were 

 found not only in the male defferent duct but also inserted into the 

 oviduct of the female. This interpretation of the use of the specialized 

 first abdominal legs in the Schizopoda was extended to the Petasma of 

 the Penaeidea, by Spence Bate, in the Challenger Reports Yol. XXIV, 

 p. XL VI, because the exceptionally pelagic member of the Penaeidea, 

 Lucifer^ also shows spermatophores attached to the openings of the fe- 

 male oviducts. That the plate like outgrowth of the first abdominal 

 leg of the male Lucifer is used to transfer the spermatophore to the 

 female is, however, still inferential. Professor W. K. Brooks who 

 had the best opportunity to study the living Lucifer ^ states in the Phi- 

 losophical Transactions of the Royal Society, 1882, p. 59, „I was unable 

 to discover how the spermatophore is transported to the body of the 

 female , or what part the clasping organ upon the first pleopod of the 

 male performs during the act of copulation." 



Spence Bate has nothing to say as to any possible use of the pe- 

 culiar female organ, the Thelycum. 



In his monograph on the Crustacea in Bronns Klassen und Ord- 

 nungen, A. E. Ortmann discusses the peculiar organs of the Penaeidea, 

 and concludes that the Petasma and the Thelycum may be used together 

 in copulation. On page 1070 he says: »Die Bedeutung, die diesem 

 ^Thelycum'' zuzuschreiben ist, ist noch sehr unklar, doch dürfte es sich 

 vielleicht nachweisen lassen, daß die Bildung des Thelycum bei den 

 einzelnen Arten in direkter Beziehung zu der ebenfalls mannigfaltigen 

 Ausbildung des männlichen Organs {Petasma) steht, und daß beide bei 

 der Copulation benutzt werden, i^immt man nämlich an, das beide 

 Organe, das männliche und das weibliche, sich bei der Copulation ver- 

 einigen oder aufeinander legen, so kommt dadurch die männliche Ge- 

 schlechtsöffnung ziemlich genau der weiblichen gegenüber zu liegen. 



