206 repobt — 1878. 



the vitellus appears to divide into larger masses, each mass being the con- 

 gregation of a number of cells adhering together by compression, as if 

 the cells had increased in size and with the increase enforced a correspond- 

 ing pressure against each other ; each cell, moreover, contained within 

 itself a number of smaller ones. 



The vitellus at a not very distant period becomes transparent, accord- 

 ing to our observation, at one spot (PI. VII., fig. 2a) on the margin. 

 When viewed laterally, it appears like a line of clear fluid near the chorion, 

 while the cells of the vitellus that are in contact with it have become 

 large and transparent, but tolerably even along its margin. This line 

 extends along the surface and deepens towards the centre. Later and 

 closer inspection shows that this transparent region extends to some 

 depth below the surface, and continued examination demonstrates that 

 it is progressive, so that the vitellus, while united at one point, is so 

 deeply divided at the opposite, that it appears to cover the embryo on 

 each side. Soon the cells appear to congregate together into lobes and 

 film over with a skin of extreme tenuity ; but these lobes, a, b, c, upon 

 inspection are repeated on each side, while a central one occupies a space 

 between them, while another, more important, is also apparent in the 

 same line ; all these are, at this stage, nearly equal in progressive de- 

 velopment, the two central being perhaps the largest, certainly the longest. 

 (PI. VII., fig. 3.) 



Soon after, three or four smaller lobes are seen to be formed in a con- 

 tinuous line with the preceding marginal ones, at this early stage the last- 

 named central lobe may be observed to divide into two equally prominent 

 ones at its extremity. A little later and all the several lobes become 

 clearly defined. The four latest pairs that appeared are less massive than 

 the three previously existing pairs, and the whole, even at this early 

 embryonic stage, may from their relative position and arrangement be 

 detected in their connexion in the advanced embryo. (PI. VII., fig. 4.) 

 The three pairs of lobes that were first brought into existence are more 

 massive and globular in their appearance. They are marked a, b, c, in 

 the figures, and very soon may be observed to assume definite forms. 

 The first (a) is rather long and compressed. The second (b) globular 

 at one extremity but apparently extended at the other ; while the third 

 (c) is extended and bilobed at its extremity. Under a slight compres- 

 sion these distinctions of form become readily appreciable to observation. 

 It is within our power to determine with confidence at this early 

 stage that these three pairs or sets of lobes occupy the position of the 

 future organs (a) of vision and antennge (b and c). The great central lobes 

 that separate them, and which in the decapoda approach each other, cor- 

 respond, the one to the labrum, the other to the terminal extremity of the 

 animal ; and the three or four smaller lateral lobes (d, e, f, g) that appear 

 a little later correspond with the oral appendages of the future animal. 



Having ascertained in this incipient condition the relation of the first 

 croup of three anterior pairs of lobes to the appendages of the adult 

 animal, and observed how closely these lobes correspond with each other 

 at first, and how they vary and become distinct from the succeeding, — 

 a distinction that is suggestive of their being a separate group of append- 

 age^ — leads to the conviction that they correspond with the three an- 

 terior pairs of appendages in the earliest or nauplius form of Crustacea, as 

 they exist in the brephahis of the Cirripedia. 



To strengthen this idea and give it demonstration, take the small dark 



