526 CKESSWELL SHEARER AND DOROTHY JORDAN LLOYD. 
mol’phosed within a shorter time than eiglit weeks, and 
usually have taken at least ten weeks. Again, the develop- 
ment of the parthenogenetic larvm is never as regular as 
that of the normal ; the arms tend to grow somewhat irregu- 
larly from the first, as a glance at the figures will show. 
It is remai’kable, however, that a large number of these 
irregular larvte are quite healthy, and form perfect Echinus 
rudiments, and may metamorphose into A’oung sea-urchins. 
While in the normal larvae, abnormality of growth is usually 
a sign of early death and inability of the larvm to reach a 
late stage, in the parthenogenetic, it seems to have no such 
significauce. The irregularity of these larvrn seems most 
marked in the order in which the arms appear. This often 
gives them a peculiarly abnormal appearance. It has to be 
borne in mind, however, that this is sometimes seen in healthy 
larvte obtained from tow-nettings, and is, perhaps, of no great 
significance. Another feature presented by the partheno- 
genetic plutei, is that once they have begun to form their 
Echinus-rudimeuts, the rest of the pluteus rapidly degenerates 
and begins to lose its arms. Thus, by the end of the third or 
fourth week, the parthenogenetic plutei ai-e quite different in 
appearance from the normal ones, in that their arms have 
already undergone considerable degeneration, while their 
Echinus-rudiments are still small; the normal larvae of the 
same age have perfect arms, and large Echinus-rudiments. A 
frequent abnormality of the parthenogenetic larvae is a peculiar 
crumpling in of the dome of the pluteus, shown in fig. 22. 
This abnormality has appeared very often in our cultures. 
The remarkable rate of growth of the parthenogenetic 
plutei in the early stages is in marked contrast to their 
slow growth in the later stages. As the time for meta- 
morphosis approaches they become more and more feeble, 
and in the last stage of metamorphosis they seem unable to 
absorb the remnants of the pluteus. They may remain 
in this condition for weeks, until they finally die from the 
interference of the still attached remains of the pluteus. The 
spines and pedicellarim can be seen protruding through the 
