NO. 1846. ON CERTAIN ELEUTHEROZOIC PELMATOZOA—KIRK. 103 



over any given area of sea bottom would not be of long duration, the young from the 

 embryos which happened to fall at any given place would naturally be all of approxi- 

 ■ mately the same age, and hence of the same size. 



Tliis casual peppering of eggs seems opposed to all that we know 

 of the habits of the Crinoidea, and would furthermore be liighly 

 detrimental to the best interests of the organisms. In the fu^st place, 

 fertiUzation would by no means be assured, and, in the second place, 

 the chances are that the majority of the eggs would fall in an unfav- 

 orable environment. 



Such an hypothesis fails to explain the colonies of young indi- 

 viduals as it is supposed to do. Were the adult colony to stop at a 

 given spot and discharge a large number of eggs, and subsequently 

 were the eggs to develop and furnish young that acquired freedom 

 at the same time and were imbued with the colonial habit, one might 

 perhaps concede that tliis explanation explains the conditions as we 

 find them. There are too many difliculties in the way, however. 



On the other hand, the swarming of the crinoids in the breeding 

 season certainly forms a plausible solution of the problem. One 

 would expect crinoids of the same age to interbreed, and so we 

 should expect to find any given colony composed of individuals of 

 approximately the same size. There should be at least two or three 

 distinct grades. The first would consist of year-old animals perhaps. 

 The next year the crinoids might be of suflicient size to herd wdth 

 the adults, although there may be a second-year group as well. A 

 comparison of the size of individuals in different colonies might be 

 used as an approximate index of the rate of growth of the animals. 



As to the life history of Uintacrinus one can not be certain. It is 

 probable that the eggs were laid in shallow, comparatively current- 

 free water. Here they hatched and the larvae become attached to 

 the bottom. There seems no question but that a stalked stage was 

 had, although, as will be noted below, exception has been taken to 

 this view. Upon becoming detached from its column the young 

 Uintacrinus probably remained in the shallow water of the embay- 

 ment. It is probable that the first j^ear at least was passed here, the 

 animal not having sufficient swimming powers to reach the open sea. 

 Such embayments could have but feeble currents, and the animals, 

 in order to get from place to place, must have had to rely to a con- 

 siderable extent on their own activity. 



Clark, in the passage quoted above, speaks of the young Uinta- 

 crinus as discarding their stems. In a paper published at approxi- 

 mately the same time as the one quoted he has this to say: "The 

 crinoids are the only recent fixed echinoderms; but in the fossil 

 crinoids, as Lang pointed out in Marsujntes, and I independently 

 showed in Uintacrinus, there are forms which exhibit no evidence of 

 having been attached; in fact the evidence is quite the other way. 



