Embryology. 471 
thesis of Lankester of the homology of the lungs and tracheæ of 
spiders with the gills and gill-appendages of Limulus. 
Among the conclusions which are drawn, the following are worthy 
of note. The yolk-cells of hexapods and spiders are regarded as 
the true endoderm, but their purpose is the digestion of the yolk. 
The functional endoderm is of later origin, and forms the epithelium 
of the digestive tract. Spiders and the Merostomata are allied to 
each other, and differ from other arthropods in the absence of 
antenne. The tracheæ of hexapods and of spiders are not homolo- 
gous ; for in the one they are clearly modified appendages, while in 
the other they occur on segments where well-marked appendages 
exist.—J. S. K. 
THE DEVELOPMENT OF CrANGON.—In continuing my studies 
of the ontogeny of Crangon, I find the following points worthy of 
presentation, apart from my complete paper, soon to be issued. The 
blastopore, contrary to my previous statement, never becomes com- 
pletely obliterated, but persists, and later an in-pushing takes place 
from the same spot and gives rise to the proctodeum. 
he anus is at first dorsal in position, and attains its ventral 
position later by an outgrowth of the telson. 
In front of the anus are a number of large budding-cells, both 
ectodermal and mesodermal, and from these are budded off new 
cells, which give origin to the segments of the body. They con- 
tribute largely to the nervous system and myotomes, and in them 
occur the only cases I have seen of karyokinesis in Crangon. They 
may be compared with the mesoblasts and neuroblasts of the leech, 
as described by Dr. Whitman. | 
The alimentary tract proper is wholly of ectodermal origin, 
the proctodeal` and stomodeal inpushings, giving rise to 
all of it. The endoderm of invagination forms first migratory yolk- 
cells, which metabolise the yolk, and, later, arrange themselves 
— = epithelium of the so-called “liver” or mid-gut gland of 
renzel, 
The green gland is of mesodermal origin, as maintained by 
Grobben, and not of ectodermal, as described by Reichenbach and 
Ishikawa. This allows of its comparison with the segmental organs 
of the annelids. These points will be fully illustrated in the 
complete paper.—J. S. Kingsley, Bloomington, Ind. 
