56 M. E. Besscls on the Species of Atux 



recently A. Brandt lias studied the develo])niental history of 

 the Lilxdlidida; and Ilemiptera with special reference to the 

 embryonal envelopes. 



The Acarida;, however, had not been taken up by any one 

 in the manner re(iiiircd by the ])resent state of science. For a 

 consid(;rabh; time I had taken pity upon these neglected crea- 

 tures, and investigated the development of yl /«./■, Phytojms^ 

 Tetranychus telarius^ Sarcopten^ and some other forms. When 

 I was on the point of publishing my results (I oidy waited for 

 the beginning of May in order to till up some deficiencies in 

 the development of Phytopus)^ I was not a little surprised at 

 finding in the last part of Sicbold and Kfilliker's ' Zeitsehrift' 

 a memoir by ClaparcMJe*, e]a])orat(!d in his usual masterly 

 manner, which rendered the ])ublieati(ni of the developmental 

 history of those species whieh L had investigated in common 

 with (Jla])arc!dc almost superfluous, inasmuch as our results 

 essentially agreed. 



Tiie develo])ment of Atax ypsilophorufi^ some points in 

 which will be here indicated, was described in its l)road fea- 

 tures by P. J. van 15eneden as early as the year 1848t. liut 

 precisely the most remarkable cirenmstances escaj)cd that 

 observer, otherwise so accurate ; and this may be due to the 

 fact that he [jrobably made use of a different egg for the in- 

 vestigation of each stage of development. In a letter which 

 I sent to Van Beneden at the beginning of September 1868, I 

 mentioned, en passantj that the r(;sults which I had obtained 

 with regard to the development (){ Atax could not be brought 

 into accordance with his. In connexion with a memoir u])on 

 the spherical organ in the AmphipodaJ (sent to press in No- 

 vember 18r)8), I mentioned the occurrence " of an embryonal 

 envelope of extremely peculiar characters in the species of 

 Atax from Unto and Anodonta^'' and also the amoeboid cells 

 fcmnd between this envelope and the embryo, which are called 

 haiiiuimccba! by Claj)art!de. 



As has already l)('en stated, my results agree witli Claj^a- 

 rbde's in all the })rincipal ])oints. ]n the observation of tlie 

 formation of the blastoderm, however, I have been rather 

 more fortunate than the above-named naturalist, who was un- 

 able to observe that process. How long after the dejjosition 

 of the eggs the blastoderm makes its appearance, no one can 



• Stmlion an Aoarirlcn, pp. '4J/5-/54(;. 



1" " IJcclicrchcs .Miir I'llistoiro natniello ct lo D^veloppement de VAtax 

 ypsilophoru,'' Mt'nioireH dv rAcnd. Ivoy. de J5elgique, tonic xxiv. 



\ " ]'iini^<! Woil(^ iibcr die I'liitwickt'liingsgcscliichte und den morplio- 

 lofrischen Werlli der kii<;eirdniiif,'en Orji'ane der Anipliipoden," .lenaische 

 Zeitsc'liril't fiir Medicin und NalurwiHseneliai'len, Jid. v. Jli't. 1. p. i»8. 



