Ill 



REPRODUCTIVE CELLS 



Embryology. — The study of the manner in which reproductive cells, 

 through multiplication, specialization and organization, incorporate new 

 matter and energy and grow into new individuals similar to their parents 

 is embryology, ontogeny or developmental history. This is the main 

 subject of Part I of the present work. 



As a brief forecast of the process of individual development it may be 

 stated that it begins with the fertilized egg or odsperm (ova-sperm, Plate I, 

 fig. 1) as the simplest form in gross structure assumed by the individual 

 at any period in the whole cycle of its life-history. The oosperm by suc- 

 cessive divisions soon gives rise to a simply constituted cellular organism, 

 the embryo (figs. 2-8), and shortly afterwards to a more highly organized, 

 swimming a'nd creeping, feeding and growing, young animal, the larva, 

 (figs. 9-21). At the end of a period of free life the larva settles on to some 

 solid object, such as a rock or shell, fastens its own minute shell thereto, 

 and becomes a spat (fig. 22), which has but to grow (Plates II and III) and 

 complete its organs to become an oyster. When it reaches a size of about 

 one inch in length (Plate III, 4th line and 1st fig.) the young oyster begins 

 to produce sperms or eggs (Plate VII, fig. 20) of a new generation. Egg, 

 odsperm, embryo, larva, spat, oyster, and again the egg, are the chief 

 stages in the cycle of development. 



Any account of the development of the oyster always remains to some extent im- 

 perfect. What is regarded as complete for the time is obtained by fitting each newly 

 acquired fact into its proper place among those already known, in such a way that the 

 whole makes a continuous and reasonable story. The progress towards completeness 

 in the narrative is as much a development as are the events described. 



The older naturalists, zoologists, or embryologists had to content themselves with 

 few facts and employed but few descriptive terms. The meaning of the word "egg" 

 was often extended to include embryonic and even larval stages; the word "embryo" 

 comprehended larva and even spat; "spat" was applied to swimming as well as fixed 

 stages. This indefinite mode of description corresponded with the knowledge of the 

 time. When we consider the inexperience, disadvantages, want of appliances and lack 

 of methods, we can freely forgive their errors and feel grateful for the information and 

 theories they passed on as a guide, and incentive to further research. 



But when we turn to works of the present day we look at least for sufficient re- 

 search to distinguish facts from fancies, as well as for a plain, direct and unambiguous 

 statement of observations and their apparent bearings — in short, for a scientific method. 

 Some of the hastiness of observation and conclusion, as well as looseness in the appli- 

 cation of terms, in America, comes from a too confident expectation of the same con- 

 ditions and phenomena as have been observed in Europe and the application of terms 

 already in use in European literature. 



Our oyster is of a different species from the European oyster and there are some 

 remarkable differences in the development. The most important of these is that in 

 our oyster the ripened eggs are discharged at once into the sea, outside of the mother 

 oyster, where fertilization and all stages of development take place. In the common 



