Organs of Invertebrate A nimals. 5 3 



seminal receptacles. And this, too, is now known 

 that the part which was long regarded, either as a 

 special parasite, or else as the male octopus himself, is 

 nothing else than the sexual arm of this creature, 

 detached from the body, and adhering by its suckers to 

 some part of the mantle of the female octopus the 

 case of this sexual arm being in reality not unlike that 

 of the spermatophorous limbs of the male of the cyclops 

 and of some other entomostracan crustaceans. Nor is 

 there anything exceptional in the organs which do duty 

 as ovipositors. In the wasp, for example, these are 

 made up of two long, sharp, slender blades, with 

 serrated edges, which are closely opposed in the act of 

 piercing, and which are afterwards separated so as to 

 leave an inter-space for the passage of egg or poison 

 as the case may be. The resemblance between the 

 parts which serve as ovipositors or stings, one or both, 

 and the long sharp lancet-like oral appendages is not to 

 be mistaken. This may not be quite so close as that 

 which exists between the cephalic and caudal suckers 

 of the leech, but it is scarcely less so : and so, after 

 what has been said, it is scarcely possible to avoid 

 coming to the conclusion that the external genital 

 appendages, male and female, are in their nature true 

 limbs modified so as to answer a particular purpose, and 

 also that there is a tendency to a repetition of these 

 limbs in the same form at each extremity of the trunk. 



And thus, as in the various limbs of vertebrate 

 animals so in the various appendicular organs of inver- 

 tebrate animals, it is possible to assert positively that 

 unmistakeable traces of unity are to be detected every- 

 where. 



