320 EMBRYONIC DEVELOPMENT 



XII. THE LARVA. 



The larva retains the plastic nature and assumes the polymorphic outlines which 

 we have noticed in the embryo. The preponderant forms assumed are already fore- 

 shadowed some time before the latter breaks the outer envelope (fig. 84 — 91 ). It still 

 moves with all degrees of velocity, mayhap more rapidly, being now free from all 

 obstacles and allotted to steer in almost any direction which opens itself before it. 



The forms, however, of the larva are not quite as diversified as were those of the 

 embryo. Its plasticity is more of a temporary character, affecting rather the regions 

 one after another, than the general outline itself. 



A few days after their breaking out of the egg, the larvae appear under two typic 

 shapes. In one the back or middle upper region is concave, whilst both extremities 

 are somewhat elevated; it has a camel-like outline (fig. 94). In the other, the back 

 is convex, very elevated and both extremities declivous ; the outline is dromedary-like 

 (fig. 99). In both forms the sides are rounded, and the anterior region is much nar- 

 rower than the posterior one, as exhibited by the figs. 95 — 98 and 100 — 103. The 

 under part of the body does not differ otherwise from its appearance in the embryo, 

 except that the grooves are deeper, and consequently rendering the hillock-like eleva- 

 tions more prominent, making the animal to appear as if supported by three pillars or 

 columns (figs. 96 and 103). In both forms also, cases may occur, which are al- 

 ready to be observed, though but slightly indicated in the embryo, in which the an- 

 terior region is divided, causing four of these pillars or processes to be present. Figures 

 of these were not deemed necessary; fig. 85 conveying a correct idea of the fact here 

 alluded to. When such, however, happens to be the case, the anterior region is as 

 broad as the posterior one. 



The rapid motion of the larvse, prevented my seeing them either at rest or even 

 permanently, in the focus of the microscope; their small size requiring a high 

 magnifying power, reduced considerably the field of vision. Attempts at fixing 

 them between two glasses proved unsuccessful : the little creatures being constantly 

 crushed under the slightest pressure. Hours after hours were spent, the eye over the 

 microscope, in order to form a complete idea of their outlines, until I was prepared to 

 carve models of their shapes, from which models, figs. 94 — 103 inclusive, were drawn 

 . by Mr. A. Sonrel. This circumstance is mentioned to account for their artistic ap- 

 pearance ; also to explain their being mere shaded outlines, without any attempt for 

 exhibiting their structure. As copies, in natural size, of my models, they are propor- 

 tionally a little larger than the other figures. 



The body of the larva is semi-transparent, in which no organs are as yet to be dis- 

 covered ; the eye-specks alone, dark brown, are very conspicuous. Vibrilloe still cover 

 the whole surface of the body, but are especially developed around the prominences of 



