er Zn 
Normal Plates of the Development of Squalus acanthias. 69 
infra-orbital (On.inf.-or.), hyoid (On.hyo.), infra-rostral (On.inf.-ros.) and medial (Cn.m.) canals are present. Long 
gill filaments project from all of the gill slits. The heart shows a marked dilatation of the bulbus cordis 
(B.cor.) already mentioned as characteristic of embryos of about this stage. The lateral lobes of the 
liver (L.) are now enormously increased in size, and extend backward to the sixth turn of the spiral valve. 
A small tongue-like projection from the median lobe overlaps the right side of the base of the vitelline duct. 
The ventral lobe or head of the pancreas (Panc.) and the pancreatic duct are seen on the left side of the 
intestine above the first turn of the spiral valve. The spiral valve (Sp.v.) makes fourteen complete turns. As 
compared with the preceding embryo the greatly increased breadth of the intestine is noticeable. Between 
the last turns of the spiral valve and origin of the digitiform gland the intestine is much constricted. 
(See normal tables, p. 37.) Again behind the point of origin Rp. fee 
of the digitiform gland (.Dig.gl.) the intestine passes into a en 
constricted portion which in turn leads into the cloaca. 
The cloacal plate (Ol.p.) is lenticular in outline and is a 
bounded by rounded arches, the beginning of the claspers. a 
m.pre-0 
On.eth. 
Rp. Mo. 
Cn.inf.orb. Lp. 
On.pre-o Bro 
At. 
v. 
S.trans. 
37% 
Ton? 
Deren 
REN) 
V.subint. 
Fig. 25. Fig. 26. 
Fig. 26. Dissection of an embryo 37 mm. in length, corresponding to normal plate series No. 32. X 6. 
In this embryo nasal flaps are completely formed, and the lateral line system somewhat further 
developed than in the embryo of the preceding dissection. The labial pockets (L.p.) well established. The 
gill filaments are in about the same stage of development as in the preceding dissection. The pericardial 
cavity is now reduced in size as compared to the preceding dissection. The bulbus cordis (B.cor.) is 
