A Contribut. to the Embiyol., Life-history, and Classificat. of the Dicyemids. 55 



pod to another , and hence it remains doubtful whether ali , or even the 

 chief events of reproductiou take place within the renai organ. Viewed 

 eomprehensively , and without reference to detail, what we actually 

 know aboiit this matter may be briefly summed up as follows : 



1 . Two kinds of embryos , dìfifering very widely from each other 

 in structure, form, size, and development. are set free within the renai 

 organ of the Cephalopod. 



2 . Both sorts of embry os originate in a single pareutal form , and 

 not in two unlike individuai» as hitherto supposed. 



3. The vermiform embryo develops directly into theadult; 

 the fate of the i n f u s o r i f o r m embryo remains stili a matter of pure 

 coujecture. 



4. Although ali adult Dicyemids of the same species are alike in 

 structure, and essentially so in form, size, etc., they do not all take 

 a like share in the work of reproduction. Some produce only one kind of 

 embryo, and may therefore be called monogenie; others produce, 

 successively, both sorts of embryos, and on this account may be named 

 diphygenic'. 



5. Both monogenie and diphygenic individuals develop from the 

 same kind of germ-cells, and no distinction between them arises until 

 they begin to reproduce. 



6. In monogenie individuals, the germ-cells, after a period of mul- 

 tiplicative di vision, develop into vermiform embryos. 



7. In diphygenic individuals, after a much shorter period of mul- 

 tiplicative di vision, each germ-cell eliminates a nucleus-like corpuscle, 

 and then develops into the Infusorigen, a group of cells comparable to 

 the Gastrula of the vermiform embryo. From one to eight Infusorigens 

 are found in one Dicyeraid. The Infusorigen, after producing a certaìn 

 number of germ-cells that give rise to infusoriform embryos , resolves 

 itself into cells destined to produce vermiform embryos. The develop- 

 ment of both kinds of embryos is completed within the individuai which 

 produced the Infusorigen. 



The Infusoriform Embryo. — As vermiform embryos devel- 

 op directly into adult Dicyemids, and as the multiplication of individ- 

 uals within the host seems to be thus fully provided for, it has been 

 generally assumed that the infusoriform embryo , which is not known 

 to fulfill auy co-operative purpose, serves the important end of carrying 

 the species from host to host. 



òicpuTj?, of a two-fold nature, or form, and Y^^^vàv, to produce. 



