K |> L 



Fig. 159. 



as in the third stage strongyloid larvae, hence strongyli- 

 form. 



Litt'e is known regarding the character of the esophagus 

 of the fiist stage larvae of spirurins. In the first stage 

 larvae of the genera Ascarops and Gongylonema Alicata 

 (1935) found faint indications of a division into corpus, 

 isthmus and bulbar region (Fig. 157 D) which entirely 

 disappear during later stages and are replaced by a divi- 

 sion into a short narrow anterior part and a long, wide 

 posterior part, both parts being cylindrical. The first 

 stage larvae of mermithids (Agamermis decaudata) may 

 have an esophagus consisting of five regions; (1) and 

 (2) equivalent to corpus, (3) a narrow part (? isthmus), 



(4) a swelling and (5) a long narrow posterior part. Two 

 small subventral and a large dorsal esophageal gland 

 are situated posterior to (4). In addition, two subventral 

 rows of eight smaller cells, the stichocytes are situated 

 along side the posterior narrow region (Fig. 93). 

 During later development the esophagus narrows, the 

 anterior swelling (2) disappears and the posterior part 



(5) becomes more or less surrounded by the large pare- 

 sophageal body, the stichosome, which retains the two- 

 cell-row form throughout later development. Each stich- 

 ccyte is a large unicellular gland with a separate orifice. 

 The three original esophageal glands atrophy after the 

 nematode enters the host (See p. 92). 



Very little is known about the esophagus of 

 first stage Trichuris larvae but Fuelleborn (1923) 



Genital primordia. A — Srculynema rigid-urn ; B-C — Rhabdias bufon- 

 is. D-H — Rhabditis aberrans, I-J — Allanto>iema tnirabile. K-L-N — 

 Bradynema strasseni. M — Alllmtonema mirabile. All from Musso, 

 1930, Ztschr. Wiss. Zool.. v. 137 (2). A, After Zur Strassen, 1892. 

 B-C, after Neuhaus, 1903. D-H. after Krueger, 1913. M, after 

 Wuelker, 1923. 



illustrated it as being composed of an anterior 

 part terminated by a glandular swelling and a 

 posterior part extending between two rows of stichocytes. 

 According to Wehr (1939) the esophagus of the first stage 

 larva of Capillaria columbae consists of a long narrow 

 anterior part, a slight swelling and a cell body, or sticho- 

 some region, consisting of a. double row of seven sticho- 

 cytes (Fig. 163 0). In the late first stage the stichosome 

 has greatly increased in size and number of cells (Fig. 

 163 P). By the third stage the two rows have fused 

 forming a single row of cells (Fig. 163 Q). Th? approxi- 

 mate ratios of the length of the esophagus to the length 

 of the intestine in each stage were given as follows: 

 First staige 3. 5 : 1 ; Second stage 2:1; third stage 1. 8 : 

 1; fourth stage, 1. 1 : 1 and adult, 1 : 1.4. 



Considering the esophagi of both trk-huroids and 

 mermithoids it seems reasonable to conclude the double 

 row stielnsome of first, stage trichuroid larvae is palin- 

 genetic. The intraesophageal character of the primary 

 esophageal glands of trichuroids is undoubtedly primitive 

 while their extraesophageal position in mermithids is 

 recent and their hypertrophy at the period of-penetration 

 must be considered cenogenetic. 



Intestine. Information on the postembryonic develop- 

 ment of the intestine is strangely lacking. A few bold 

 writers have admitted the presence of cells in the intestine 

 but as a rule the intestine merely forms a connecting link 

 between esophagus and rectum. However, changes both 

 interesting and extensive do occur in some forms. In the 

 more primitive nematode g-roups the multiplication of 

 cells must be very limited and sometimes is probably 

 confined to certain regions of the intestine. This appears 

 to be true of most rhabditids, oxyuroids and similar 

 forms. Numerous cell divisions must take place in the 

 more highly evolved aphasmidian forms and in ascaridoids, 

 spirurins, trichuroids and dioctophymatoids. The inte:- 

 tine of first stage Asccn-is himbrieoides consists of innu- 

 merable cells. According to Moorthy, 1938, the intestine 

 of the late first stage larva of Camallanus sweeti has about 

 35 cells, the number increasing until in the early adult 

 stage there are about 200. The same author rec-ords 12-15 

 cells in first stage Dracuncitliis medinensis while in the 

 late third stage there are 35-40 cells. Of strongylins, 

 known to possess few intestinal cells in the adult stage, 

 Lucker (1935, 1936, 1935) offers considerable information. 

 Cylicodontophorus bicoronatus, Cylicocercns pateratus 

 and Cylicocyclus insigne, each have only eight intestinal 

 cells in the infective larvae while the genera Gyalocephalus 

 and Strongylus have 12 in the first genus and 16 to 32 

 in the latter. Lucker also definitely established the exist- 

 ence of a lumen in those species with an eight cell intestine; 

 according to his observations the intestine of second stage 

 larvae of these forms have a 22 cell intestine, the number 



233 



