No. 2.] BLATTA AND DORYPHORA. 365 
mesoderm, one on each side projecting into the body cavity. 
Later (Fig. 84 gz) they become rounded and are attached by a 
thin band of splanchnic mesoderm only. I have seen the much 
attenuated duct leading from each organ to the exterior, but 
have made no observations on its origin. The ducts converge 
posteriorly, but end by separate openings on the 11th abdominal 
somite; thus presenting a condition which in Ephemerids is 
permanent throughout life, according to Palmén (37). There 
is probably some connection between the two pairs of very 
indistinct tracheal openings in the 1oth and 11th somites and 
the openings of the efferent ducts, but I was unable to deter- 
mine whether the large sexual openings originate by enlarge- 
ment from a single pair of these tracheal openings, or from the 
confluence of all four to form two orifices. The cross-section 
(Fig. 80) includes the openings of the efferent ducts (go go), the 
knife having taken away a very thin layer of surface cells. 
Up to the formation of the coelomic cavities the mesoderm of 
Blatta closely resembles the same layer in Dorvyphora. With 
the evagination of the appendages from the entoderm a decided 
difference is, however, observable. Each coelomic segment, if 
situated in an appendage-bearing segment, instead of retreating 
dorsally as in Doryphora, sends a diverticulum into the appen- 
dage. This is clearly seen in Fig. 53 c/, a cross-section from an 
embryo twelve days old. The cells of the diverticulum develop 
into the muscles of the appendage, and together with a portion of 
the mesodermic layer still remaining in the body cavity are shut 
off from what probably represents the true coelomic cavity (Fig. 
54 c/). The further changes again resemble those in Doryphora. 
Long before the heart is formed and the lateral walls have met 
in the median line, the body walls of the embryo are observed 
to pulsate regularly like the body walls of Gryllotalpa, as 
described by Korotneff (25). As in Doryphora a plasma is at 
this time found in the body cavity which is divided by films of 
connective tissue into a great number of small intercommunicat- 
ing lacunz (Fig. 54). In regard to the primitive blood sinus, 
my observations confirm Patten’s (38). He says: “The primitive 
blood sinus is the space between the somatic and splanchnic 
mesoderm, divided into a number of smaller and irregular 
sinuses by meshes of connective tissue, some cells of which, in 
the earlier stages, become free and form the blood capsules. By 
