772 SCIENTIFIC RECORD FOR 1885. 



and in cross-sections are to be found " round these organs a layer of 

 remarkably tall pigmented cells," and '^ between these are ganglion cells 

 with prolongations directed towards the chitinous layer." These are 

 thought to be analogous to the "chordotonal organs" of insects. [Zool. 

 Anzeiger, 1885, pp. 264-266, 537, 538). 



Dimorphism in spiders. — Several observers have determined that cer- 

 tain spiders have two broods, and that the individuals of the two differ 

 more or less, in a few cases the differentiation having been considered 

 as specific. The so-called Meta segmentata and Meta Mengei, for exam- 

 ple, represent several broods of one and the same species. In other 

 cases, however, there is but little difference between the two broodf>. 

 {Zool. Anzeiger, 1885, pp. 459-464, by Bertliau ; 532, 533, by Korsch.) 



Crustdceans. 



A nervous system in the Centrogonida. — The singular degraded crusta- 

 ceans, known as Peltogaster and Sacculina, which have been ditteren 

 tiated into a distinct order called Ehizocephala or Centrogonida, have 

 a nervous system so rudimentary and obscure as to have escaped ob- 

 servation until the past year. Mr. Y. Delage resolved to supply the 

 deficiency, and after two years of observation he found it in Sacculina, 

 while in Peltogaster, on the other hand (although the absolute diflicnlties 

 of the search were exactly the same as in Sacculina) he found it in the 

 first individual dissected after less than an hour's work. He mentions 

 this particular only to show the value of the morphological method, 

 and if he found this nervous system it is by no means due to partic- 

 ular address in dissection; it is because, armed with the morphological 

 data derived from the study of Sacculina, he sought for it precisely 

 where it ought to be found. When one knows where to look for it, he 

 remarks, it is easy to iind, but this last condition is indispensable, and 

 it is from not having this requisite knowledge at their disposal that 

 the numerous authors who have previously investigated the genera in 

 question failed to discover it. The ganglia are displaced and in ap 

 parently different relations on account of the position of the ovaries 

 and other i:)arts. In these displacements, was the nervous ganglion to 

 retain the original position at the bottom of the ovary, or was it to fol- 

 low the cloaca, or the mesentery or the cement-glands'? Observation 

 has shown that it did not remain immovable ; therefore its relations 

 with the, declivous pole of the ovary are not at all essential; it had fol- 

 lowed the cloaca and the mesentery, but especially the cement-glands, 

 in their movements ; hence it is with these organs, and chiefly with 

 the last named, that it has fundamental relations. On the other hand, 

 we see that the close relations of the ganglion with the testes in Pelto- 

 gaster are quite accidental, since in Sacculina these organs are as far 

 apart as possible. Henceforward in seeking for the nervous system in 

 other Centrogonida, in which the viscera may again affect new rela- 

 tions, we see that we shall not have to pay any attention to the testes, 



