REPORT ON THE PYCNOGONIDA. 137 



quantity was limited, so I need not appeal to the indulgence of the reader on account 

 of the imperfection of my researches in this department. 



The study of the eggs of Nymphon Irevicaudatum, Miers, was the most successful of 

 all. These eggs are the largest of the species here in question ; the number of animals 

 furnished with eggs was in this species rather gi-eat ;' aud their condition was superior 

 to that of the eggs of the other species. The method I followed is weU known. I 

 enclosed the eggs (hardened with absolute alcohol) in paraffine, and coloured the sections 

 afterwards with picrocarmine. 



Fig. 3 is a cba^dng of the first stage I was able to observe. The food-yolk and the 

 formative-yolk (deuto- and proto-plasma, Ed. van Beneden) are still mixed together, and 

 the cleavage is complete. Eveiy segment is furnished with a nucleus, coloured cUstmctly 

 red by the picrocarmine, and situated ahnost in the middle of each segment. The structure 

 of the yolk particles in each segment is very curious, and probably this is caused by 

 the continued action of the alcohol. In fig. 4 I give a strongly-magnified drawing of a 

 small part of such a segment just at the border of the section. It looks as if the yolk- 

 elements had grown vesicular,— a inatter I only make mention of as the same structure 

 is no longer observed in the next stage of development of the egg. In this stage, as in 

 the foUowing, the egg is furnished with a distinct but very thin membrane.' 



The second stage I observed has the blastoderm distinctly developed. The cells of 

 which- it is composed are very much flattened, and do not show distinct limits ; a very 

 large nucleus is, on the contrary, always easily observed. Fig. 5 shows the cells as seen 

 on section, fig. 6, the blastoderm with the nuclei magnified. Every nucleus shows a 

 distinct nucleolus and numerous small granules. In this stage the food-yolk is irregu- 

 larly spUt into larger or smaUer parts, which are coloured yellow by the picrocarmine ; 

 they do not show the vesicular structure of the yolk-segments in the first stage, and are 

 not furnished with a nucleus. 



A transverse section of the next stage of development I observed is figured in fig. 7.' 

 Here the embryonic development is already far advanced, consequently I was nof able 



I The eggs oiNymplwn harmtum, N. lonyicoxa, and N. Mum were so far advanced in development that in them 

 onlv the different larval stages coiild be studied. , , , i 



^ Dohm loc. cit, p. 139, says that the egg of Pycnogmum litorale has a double membrane, and that these membranes 

 are found in the ovary, an assertion not corresponding with the observations I made on the eggs of Nymphon. 



3 Between the sUvge figured in fig. 7 and the foregoing, nimierous other stages were observed ; but m these the cel- 

 lular structure was so totally . spoiled by the action of the alcohol, that I dare not give drawings or descr.pUons 

 of them. The only means of distinguishing the embryonic cells from the deutoplasm is by the colouring of the 

 cells mth picrocarmine, and there can be little doubt that one of the first changes the blastoderm undei^^oes con- 

 i irthe'formation o'f a longitudinal thickening of it at the future ventral side of the embrya This Inckemng 

 terminates rather abruptly at the anterior end, but at the posterior end it slopes graduaUy to the imicellular_ part 

 S™ e b astoderm. Afterwards a longitudinal furrow seems to take rise in the middle of this thickemng, the inner 

 part of which is finally isolated in the form of a longitu.linal tube. I publish these details only with the strongest 

 reserve, the condition of the eggs and the circximstance that the sections are necessanly taken in quite xmcertam 

 directions, making the giving of a decided description impossible. 

 (ZOQL. CHALL. EXP. — PART X. — 1881.) 



