118 HYPOTHESIS OF THE DEVELOPMENT OF 



with those attending the production of individual organisms. 

 But it becomes something more than analogy when we have 

 learned the facts attending the embryonic development of 

 animals. First surmised by the illustrious Harvey, after- 

 wards illustrated by Hunter in his wondrous collection at the 

 Royal College of Surgeons, finally advanced to mature con- 

 clusions by Tiedemann, St. Hilaire, and Serres, embryonic 

 development is now a science. Its primary positions are 

 1. that the embryos of all animals are not distinguishably 

 different from each other ; and, 2. that those of all animals 

 pass through a series of phases of development, each of which 

 is the type or analogue of the permanent configuration of 

 tribes inferior to it in the scale. With regard to the latter 

 proposition, it is to be remarked that, while it is generally 

 true of the whole forms of animal being, it is more particu- 

 larly true of departments of the organization, as the nutritive 

 system, the vascular system, the nervous system, &c., each of 

 which is destined for a peculiar degree of development in dif- 

 ferent groups of animals, according to their needs. Speaking, 

 however, roundly, it is undoubted, respecting nearly all 

 animals, that they pass in embryo through phases resembling 

 the general as well as the particular characters of others of 

 lower grade. For example, the comatula, a free-swimming 

 star-fish, is, at one stage of its early progress, a crinoid that 

 is, a star-fish fixed upon a stalk at the bottom of the sea. It 

 advances from the form of one of the lower to that of one of 

 the higher echinodermata. The animals of its first form 

 were, as we have seen, among the most abundant in the 

 earliest fossiliferous rocks : they began to decline in the New 

 Red Sandstone era, and they were succeeded in the Oolitic 

 age by animals of the form of the mature comatula. Thus, 

 too, the insect, standing near the head of the articulated 

 animals, is, in the larva state, an annelid or worm, the anne- 

 lides being the lowest in the same class. The higher crus- 

 tacea, as the crab and lobster, at their escape from the ovum, 

 resemble the perfect animal of the inferior order entomo- 

 straca, and pass through the forms of transition which charac- 

 terize the intermediate tribes of Crustacea. The salmon, a 



