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PROF. J. D. F. GILCHRIST ON A 



of the adult, and most of the others were represented hy rounded prominences 

 provided with hairs. In a late puerulns with all the spines developed, it 

 may he observed by using a lens (though with some difficulty) that these 

 spines lie under the smooth surface of the cuticle of the puerulus. That this 

 is really the case may, however, be placed beyond doubt if sections are made 

 across the animal in a late puerulus stage. Fig. 5 shows such a section 



Fig. 5. — Transverse section of posterior margin of carapace of a late puerulus. 

 cm. 1, cuticle of puerulus ; cu. 2, cuticle of post-puerulus ; up., spines of post-puerulus. 



across of the posterior marginal spines, and it will be seen that they do not 

 affect the puerulus cuticle. It may be reasonably concluded, therefore, that 

 the puerulus stage, so far as the evidence goes, is characterised by a definite 

 number of spines on the carapace, and it may be provisionally assumed that 

 other young stages may also be determined in this way. 



What has been said of the spines of the carapace applies also to those of 

 the telson. The telson of a post-puerulus stage and its cast cuticle of the 

 puerulus stage were compared microscopically, and a very distinct advance 

 noted (figs. 6 & 7). In the puerulus there is a pair of strong spines in the 



Fig. 6. — Telson of post-puerulus. 



Fig. 7. — Cast cuticle of telson of puerulus. 



centre of the anterior end ; between these and the first marginal spine are 

 two more spines, there being a third, of small dimensions, at the base of the 

 first marginal spine and forming part of it. The marginal spines are five in 

 number, the last being indistinct. Besides these there were no others. In 

 the post-puerulus telson, however, there is a conspicuous double row of ten 

 spines running along the centre, and, on each side, three rows of less regular 



