438 SUB-PHYLUM HEMICHORDA. 
known, but from the region of the collar two ciliated 
funnels open to the exterior, and the enigmatical proboscis 
gland is possibly excretory. 
The sexes are separate. A number of simple paired 
genital organs lie dorsally in a series on each side of the 
body cavity in and behind the region with gill-slits 
(Fig. 235, &.). They open by minute dorsal pores. 
Development.—The eggs are fertilised outside of the 
body. Segmentation is complete and approximately equal ; 
Fic. 236.—Direct development of Dolichoglossus.—After Bateson. 
The mesoderm is represented by the broken dark line. 
In the upper row, from the left— 
Section of blastula ; beginning of gastrulation, Zzd., endoderm ; 
section of gastrula, 4/., blastopore; Ac., Archenteron; S.c., 
segmentation cavity ; closure of blastopore, outgrowth of five 
ccelom pouches (/¥/.). 
In the lower row, from the left— 
Longitudinal section, showing the five parts of the body cavity 
(bc.1, bc.2, bc.3) or ccelom. 
Cross-section, C.V.S., central nervous system ; Vch., notochord ; 
bc.2, body cavity in collar region. 
Section at a later stage, D.d.v., dorsal blood vessel. 
a blastosphere results; this is invaginated in the normal 
fashion, and becomes a gastrula. 
The development may be direct without a larval stage, 
as in Dolichoglossus howalevskii, or indirect with a Zornaria 
larva, as in Balanoglossus biminiensis, 
In the direct development the blastopore of the gastrula narrows and 
closes; the external surface of the gastrula becomes ciliated; the 
