NOTES ON THE EMBRYOLOGY OF LIMULUS. 
545 
of this envelope. This early moulting of a cuticle seems to me 
to be of but little importance in ascertaining the relationships 
of Limulus, for it is paralleled more or less completely in both 
Crustacea and Arachnida. The cases which will at once 
suggest themselves are those of Apus, as described by Zaddach 
(’ 41 ), and Atax, by Claparede (’ 68 ). Indeed, it might be well 
to adopt the latter author’s term deutovum for all such 
envelopes. Other cases, where the correspondence is not so 
exact (Asellus, &c.), will readily be recalled; but until a more 
definite knowledge is obtained of the exact origin of these 
deutova speculation as to their homology and meaning is 
useless. Kennel’s speculations (’ 84 ) seem poorly founded. 
The simultaneous appearance of the six pairs of ambulatory 
limbs seems equally unimportant, paralleled as it is with more 
or less exactness in either group. It merely indicates a con- 
centration of development, and the fact that through abundant 
food supply the embryos or its nearer ancestors have not been 
compelled to begin free life at an early stage. The closest 
resemblance, however, exists in the scorpions and spiders, 
where, the first pair of appendages excepted, the corresponding 
parts appear. Were Dohrn’s account true nothing more could 
be asked, but as I have had abundant material of earlier stages 
than any of his I believe that (as he suggests) he overlooked 
the first pair. I have not seen the slightest evidence in favour 
of his account. There is nothing in the development of 
Limulus that even suggests a Nauplius or a Zoea. 
The position and early appearance of the compound eyes 
suggest some points of interest. Since in the Decapod and 
some other Crustacea (Squilla, Branchipus, Tanais, &c.) the 
compound eyes are borne on stalks, which are articulated to 
the body, some morphologists have adopted the idea that 
these pedicles are homodynamous with the true limbs, and a 
few have even gone so far as to seek an “ ocular segment ” in 
the head of Hexapods. Without entering into a discussion of 
the many arguments against this view (which I believe totally 
erroneous even in the case of Squilla), I would say that I 
regard the eyes of all Arthropods merely as specialised portions 
