49 



nerative faculty does not reside at any part of the claw 

 indifferently, but in a special locality at the basal end of 

 the first joint of each of the legs. This joint is almost 

 filled by a mass of nucleated cells surrounded by a fibrous 

 and vascular band; and other nucleated cells intervene 

 between this band and the outer crust. The vessels of 

 the band pass onwards for about half an inch and return 

 upon themselves, forming loops. When a claw is broken 

 or otherwise injured and disabled, the Lobster or Crab, 

 by a violent muscular effort, casts it off at the transverse 

 ciliated chink or groove which indents the reproductive 

 segment. The new claw is developed by the multiplication 

 of cells, which are soon divided into five groups answering 

 to the five joints of the future limb : these nascent joints 

 are folded upon each other in the Crab, but extended in 

 the Lobster : in both they are at first enveloped in a sac 

 formed by the distended cicatrix ; the budding limb ulti- 

 mately bursts this cicatrix and its growth is rapidly com- 

 pleted : a great proportion of the reproductive cells contained 

 in the basal extremity of the injured limb, is used up in the 

 production of the new limb ; but a mass of them is retained 

 unchanged at the basal joint, and ready to renew the re- 

 productive process when needed. In the lower Crustaceans 

 such groups of cells are found at more numerous joints. 



Like Sars, the author of the article in the ( Medico- 

 chirurgical Review 5 observes, with regard to Professor 

 Steenstrup's account of the propagation of the medusiform 

 from the strobiliform individuals : " How these young 

 ones are developed whether from ova or from gemmae 

 he does not attempt to explain ; nor does he show, if they 

 are produced from ova, by what male influence they are 

 fertilized." (p. 204.) Steenstrup had not, in fact, any more 

 than his reviewer, recognized the nature of the process con- 

 sequent on fecundation, which carries the male influence 

 through successive generations of larvae. Yet he had per- 

 suaded himself that he was elucidating natural phenomena 



D 



