8S TOILERS IN THE SEA. 



to one thirteen-hundredth part of an inch, that is, so 

 minute that one of medium size would have a dia- 

 meter of about one three-thousandth part of an inch, 

 so that three thousand of them arranged in a line 

 would only extend an inch ; that these minute em- 

 bryos are destitute of anything like a proper cell-wall, 

 but soon after expulsion from the parent exhibit a 

 clear spot, which might casually be mistaken for a 

 nucleus, but which in reality is the rudiment of the 

 future skeleton ; these specks, or " yellow spots," 

 being seen resting in a sort of irregular layer imme- 

 diately beneath the flinty framework, or skeleton, of 

 the parent, and subsequently cast off through one of 

 the numerous openings of the shell. There is no doubt 

 about the rudimentary condition of knowledge of the 

 development of the young Polycystins from the sarco- 

 blast, for even as much as this is admitted by Dr. 

 Wallich. "Occasionally," he says, "during calms 

 within the tropics, the sarcoblasts of the Polycystins, 

 and other oceanic Rhizopods, may be taken in im- 

 mense numbers, although, owing to their extreme 

 minuteness they are easily overlooked. The profu- 

 sion, however, in which they occur, in every stage of 

 growth, affords the means of tracing their history in 

 al its consecutive phases, and it is highly desirable 

 that they should be carefully collected, and studied 

 by all who enjoy opportunities of obtaining them, in 

 their normal condition." 



