No. I.] THE EMBRYOLOGY OF LIMULUS. 55 



Owing to my inability to iind the segmentation nucleus, I am 

 unable to say with certainty to which of the types the egg o£ 

 Umls sholld be referred, but all the facts pomt towards the 

 ^ec:nd medication of the ectolecithal type However, seg- 

 mentation is at best an uncertain guide to affinities. 



The matter of differentiation of the S-™ W-^""":! 

 important. Until recently delamination was believed o be 

 confined to the Ccelenterates and a few other forms.' It would 

 appear however, that delamination is of frequent occurrence in 

 the Imchnid phylum. Morgan finds in the Pycnogomds ('90) 

 ':r^e multipolar delamination. and he uses this as one reason 

 for assigning these forms to a position near the Arachnids. 

 He refers to Chehfer as described by Metschnikoft and to 

 B^four-s account of Agelena, and to these additional references 

 . T hoe. r^t-. nA-nt\ clearly confirms balrour 



may be given. Locy ('86, pp. 74-/5; cieany 

 To 'far a's Agelena is concerned Henking W des„ib a 

 delaminate type of blastoderm formation in *e Jha an='d^. 

 while Faussek ('91). studying the same forms, is m full accord 

 Id expressly uses the term delamination in this connect on. 

 Schimkewitch ('84 and '<^) also clearly describes delamination 

 in Eneira, Pholcus, Agelena, and Lycosa. 



OnTe other hand, the following forms have the yolk at one 

 time free from nuclei, and hence, if delamination occur in con- 

 nection with the primitive keel, it is not of that type which 

 obrinsTn the cases mentioned above: Theridion Monn, 

 "a" at the 128-cell stage ; a Japanese species of Agelena (Kishe- 

 nouye '90), Scorpion (Kowalewsky and Schulgm, '86; Laurie, '90). 

 So ar I know, nothing approaching delamination occurs in 

 the Crustacea, while that in the Trache^es already referred to 

 is of a character far different from that in the Arachnids^ 

 Hence Limulus. in the method of differentiation of en oderm 

 from ecto-mesoderm, finds its closest analogues within the 

 Arachnid phylum. 



,esu,.ea r.o. a „lpa,io„ ol .He blas.o.e.es ,o on. po|e <^^Jl^^^^^ 

 Worms me .hat, according to his observauons <>" J°* ™'f,^^, ^^^^ „„,„ tend 

 the seementation is as I have interpreted it m this note, -a tact wn c 

 irshTtha. Bohret*y described a stage »^'-;•;^f ' -^'^ "most .Traeh- 

 . Balfour CSl). p. 278, compares the or.gm of the g"» J»)'«" ,^^„ 



eates.to a t,pe which ^PP-^^ <•; -^^"nd r" moIaSn ^an invaginat. 



are strong grounds for regarding it as a sei-oiiu ^j 



type." 



