The Embryology of Chlamydoselachus 



597 



Text-figure 27 



Heads in three aspects (dorsal, lateral, and ventral) of two 25'mm. 



embryos of Chlamydoselachus. 



A after Brohmer, 1909, Text-fig. 2; B and C after Ziegler, 1908, Text-figs. 1 and 2. 



Head in Lateral View. — In addition to Ziegler's brief general description of the head 

 of his 25-mm. embryo, comparison of it in this aspect (Text-figure 27b) should be made 

 with the head of the 20-mm. specimen in lateral view (Figure 18, plate II). The head of 

 the 25-mm. embryo is filled out and rounded with the forebrain pointing downward. 

 The mouth still gapes widely. Brohmer (1909, Text-fig. 3) had a drawing made of his 

 25-mm. embryo in lateral aspect. This in its portrayal of the anterior visceral arches 

 differs somewhat from Ziegler's figure of his specimen of the same size. It is difficult to 

 understand the mode of development of the anterior visceral arches as portrayed in lateral 

 view by these two investigators. Possibly their embryos were abnormal. However, in 

 some ways they are related to what we shall find in Nishikawa's 32-mm. specimen. 



In Ventral Aspect. — There is no like view of the head of the 20-mm. embryo 

 available for comparison. This is our first description of the head of an embryonic 

 Chlamydoselachus seen from below (Text-figure 27c). The snout-like forebrain stands 

 out against the background of the larger rounded midbrain. The eyes and nasal capsules 

 show faintly. The opening of the expanded mouth is about as broad as long. The halves 

 of both upper and lower jaws are separated by fossae — the upper fossa is the wider. 

 The gill-arches are distended, and short filaments are seen on their hinder sides. The 

 pectoral-fin fundament shows traces of the basal cartilages. The yolk cord is large in 

 comparison with the size, of the body. 



