364 whitman: [Vol. IV. 



of a Turbellarian are of the same nature and equally close ; but 

 no one would in this case be likely to mistake such resem- 

 blances for homologies.^ 



In view of the fact that the spermatophores of Clepsine were 

 discovered nearly half a century ago by Friedrich Miiller, and 

 described as a '■^ phaenomenon aijiis iieque mialogon mter reliqua 

 atmnalia reperire^' and that they have since been observed by 

 Max Schultze, Leuckart, Leydig, and Schneider, it may appear 

 a little remarkable that their function should have so long 

 escaped detection. But when we consider how totally unpre- 

 pared were the minds of investigators for such a mode of 

 impregnation, we find no difficulty in understanding how it 

 comes to pass that the old belief still prevails, that all the 

 Hirudinea, penis or no penis, copulate in essentially the same 

 manner, and fecundate by conveying the spermatic fluid of one 

 individual (or of both reciprocally) directly into the female geni- 

 tal orifice of the other, thus placing it where it can pass unob- 

 structed into the so-called uterus, or, in the absence of such a 

 specialized part, into the ovarian sacs. 



While this has been, and still is, the opinion generally re- 

 ceived, the possibilities of the eggs being fertilized after deposit, 

 of self-fertilization, and of parthenogenetic development, have 

 not been overlooked. The following notes and extracts are 

 designed to give the history of the subject, and to show what 

 questions have been left unsettled. 



Historical Notes and Extracts relating to the 



Hirudinea. 



I. Clepsine coniplmiata. 



FRIDERICUS MUELLER. De Hirudinibus circa Berolinum hucusque observatis. 

 Berolini, 1844. pp. ZZy 34- 



" Cleps. complanatas, quamvis plurimas amoris tempore continua 

 attentione observaverim, coeuntes niinquarn observavi ;' sed eodem 



^ We are continually reminded that parallel development has been a much more 

 important factor in evolution than has generally been supposed. Similar bases, 

 similar needs, similar variations (because predetermined by like causes), guided by 

 parallel selective influences, which would be sustained by like environments, have 

 unquestionably resulted in numberless analogies which are usually allowed to pass as 

 evidences of genetic affinity. 



2 Braun {System atische Beschreibung einiger Egelarten,'&t.t\va., 1 805, p. 60) makes 

 the same observation. 



