NOTES ON THE EHBEYOLOGY OF LIMULUS. 
543 
The description of the development of the brain, of the eyes, 
the midgut and its appendages, the genital organs and other 
mesoblastic structures, I leave for the second part of this paper 
where will he discussed their bearings. Still a few facts may 
be of interest here, without the details which will be given 
later. 
The brain is at first separate from the rest of the nervous 
system. It arises as two halves and each lobe is divided in 
front as shown in fig. 11, presenting a marked similarity to 
that of the spiders. The mesenteron is formed from the 
central mass of yolk, the lumen appearing after the first moult 
after hatching. The diverticula of the liver arise from the 
lateral yolk masses, and the primary lobes of which it is com- 
posed are produced by the mesoblastic septa of the cephalo- 
thoracic region (fig. 13). After the stage where we left the 
oesophagus on a preceding page, it continues to elongate and 
joins the midgut soon after the lumen in the latter begins to 
appear. It is at all times much longer than the proctodseum. 
The outer layer of the cells of the mesenteron feed upon the 
central ones, absorbing and assimilating them, thus producing 
the lumen. 
The Position of Limulus. 
Professor Lankester has so recently discussed in an able 
manner the relationship of Limulus (’ 81 ) that all that I can 
add are the few facts gained from embryology. I must admit 
that at first I was strongly inclined to regard Limulus as a 
Crustacean, but a careful consideration of the subject leads me 
to believe in its being much more closely allied to the Spiders, 
and its being a representative in the seas of to-day of the 
stock from which the Scorpions sprang. On the other hand, 
its relationships to the Phyllopods are marked ; in fact, it 
takes us back to a time when the distinctions between the 
Crustacea and the Arachnida were far less marked than they 
are to-day. The day of a belief in “ types ” is past, and yet 
some of the terminology once in vogue is convenient ; in this 
way we may still call Limulus a synthetic type. 
