TRANSLATORS PREFACE. xiii 



may contain, as it frequently does in the Echinococcus altrici- 

 pariens of Kiichenmeister, a third cyst, a " granddaughter- cyst," 

 which is also a " nurse," and thus on. 



Another curious point about all these creatures is, that they 

 are sexless. Neither cyst nor scolex-head has any sex. Nor do 

 they acquire sexuality as long as they remain in the flesh in the 

 hydatid condition. It is to this condition of the worm that Professor 

 Huxley proposes to apply the term " Agamozooid." The objection 

 to this term is, that it is equally applicable to all sex] ess forms of 

 reproduction amongst animals as to those to which Steenstrup 

 has applied the term " nurses." 



In order to acquire the conditions necessary to the development 

 of sexual organs, the cystic, or asexual form of the worm must 

 be swallowed and digested by another animal. The scolex-head 

 then becomes in its turn truly a "nurse," and this of a most 

 prolific kind, for the cyst below being displaced, the numerous 

 segments (" proglottides," as they have been called) begin to 

 make their appearance. The conditions are now such, that sexes 

 appear; each segment is merely a capsule containing a male and 

 female generative apparatus, and nothing else. Eggs, the result 

 of the union of sperm-cells and germ-cells, are now produced in 

 myriads. These pass into the external world, and being swal- 

 lowed and digested, set free the embryos, which again become 

 cystic worms as above described. 



Now these phenomena are not peculiar to Entozoa. Steenstrup 

 pointed out that they had been observed in the Medusa, the 

 Claviform Polypes, the Salpse, and the Trematode Entozoa. 1 

 Professor Owen, in the exposition of his views on " Parthe- 

 nogenesis," 2 a general term he applied to the phenomena of 

 asexual reproduction, has also given a large number of cases of 

 the same kind. One of the forms examined by Professor Owen, 



1 ' On the Alternation of Generations,' by J. J. S. Steenstrup, translated for the Ray 

 Society by George Busk. 



2 ' On Parthenogenesis ; or the successive production of procreating Individuals fronr 

 a single Ovum,' by Richard Owen, F.R.S. 



